| 1 | MD | Air Madagascar | ICAO: MDG, Callsign: Air Madagascar, IATA Prefix: 258, ICAO callsign changed from Madair | RM | AVCODES |
| 2 | MD | Air Madagascar | ICAO: MDG, Callsign: Madair, IATA Prefix: 258, ICAO callsign changed to Air Madagascar | RM | AVCODES |
| 3 | MD | FIM Air Ltd. | ICAO: FMI, Callsign: First Myanmar, ICAO callsign changed to Gecko. | MYA | AVCODES |
| 4 | MD | C&J R.R. Co. d/b/a Mississippi Delta R.R. | 7/2005; eliminated 1/2010 | | NAKINA |
| 5 | MD | Municipal Docks | 1/1980 | | NAKINA |
| 6 | MD | Municipal Docks Ry. of the Jacksonville Port Authority | 1/1975 | | NAKINA |
| 7 | MD | Municipal Docks Ry. of the Jacksonville Port Authority | Jan-75 | | NRHS |
| 8 | MD | Municipal Docks | Jan-80 | | NRHS |
| 9 | MD | *MUNICIPAL DOCKS RAILWAY, JACKSONVILLE PORT AUTHORITY (FLORIDA) | | | PWRC |
| 10 | MD | +C & J RAILROAD CO. d/b/a MISSISSIPPI DELTA RAILROAD | | | PWRC |
| 11 | MD | Municipal Docks | | | RSRV |
| 12 | MD | MISSISSIPPI DELTA RAILROAD (C&J RAI | | | SCAC4 |
| 13 | MD | Maryland - Delaware | | USA | TRAFFIC |
| 14 | MD&S | Macon, Dublin & Savannah R.R. Co. | 8/1920-10/1957 | | NAKINA |
| 15 | MD&S | Macon, Dublin & Savannah R.R. Co. | 4/38-10/57 | | NRHS |
| 16 | MD&S | MACON, DUBLIN & SAVANNAH RAILROAD CO. | | | PWRC |
| 17 | MDA | Mandarin Airlines Ltd. | IATA: AE, Callsign: Mandarin, IATA Prefix: 803, | RC | AVCODES |
| 18 | MDA | Mandarin Airlines | IATA: AE | | ICAO1 |
| 19 | MDAA | MD TRUCKING | | | SCAC4 |
| 20 | MDAC | MIDDLE ATLANTIC PRODUCTS INC | | | SCAC4 |
| 21 | MDAD | MIDDLEBURG PROPERTIES LIMITED | | | SCAC4 |
| 22 | MDAD | Miami Dade Aviation Department | | USA | TRAFFIC |
| 23 | MDADE | Miami-Dade Transit | | USA | TRAFFIC |
| 24 | MDAE | MARTINEZ, DORA E | | | SCAC4 |
| 25 | MDAF | MID AMERICA FREIGHT SYSTEMS LTD | | | SCAC4 |
| 26 | MDAI | MAINLAND TRANSPORT LTD | | | SCAC4 |
| 27 | MDAM | M & D TRUCKING CO INC | | | SCAC4 |
| 28 | MDAO | MID-ATLANTIC LOGISTICS COMPANY | | | SCAC4 |
| 29 | MDAQ | MDI TRANSPORTATION SYSTEMS INC | | | SCAC4 |
| 30 | MDAS | MIDAS EXPRESS, INC | | | SCAC1 |
| 31 | MDAS | MIDWAY TRANSPORTATION INC | | | SCAC4 |
| 32 | MDAU | MEDAFRICA LINE S P A | | | SCAC4 |
| 33 | MDAW | MODEL DAIRY LLC | | | SCAC4 |
| 34 | MDAX | Merchants Despatch Transportation Co. | added 1/1962; 7/1965-1/1980; eliminated 7/1985 | | NAKINA |
| 35 | MDAX | Merchants Despatch Transportation Co. | added 1/62; 7/65-1/80 | | NRHS |
| 36 | MDAX | MERCHANTS DESPATCH TRANSPORTATION CORP. | | | PWRC |
| 37 | MDAX | Merchants Despatch Transportation Corporation | | | RSRV |
| 38 | MDAY | MOLIVA DENIZCILIK AS | | | SCAC4 |
| 39 | MDAZ | MERIDIAN AGGREGATES | | | PWRC |
| 40 | MDB | Monde Air Charters Ltd. | Callsign: Mondeair Cargo, | GB | AVCODES |
| 41 | MDB | Vertical Aviation, LLC | Callsign: Marianas, | USA | AVCODES |
| 42 | MDB | Monde Air Charters | | | ICAO1 |
| 43 | MDBA | MARINER DISTRIBUTING COMPANY AND ANCHOR DISTRIBUTING COMPANY | | | SCAC1 |
| 44 | MDBA | MDT | | | SCAC4 |
| 45 | MDBB | MCLAMB, DENNIS INC | | | SCAC4 |
| 46 | MDBD | MCBRIDES DELIVERY SYSTEMS INC | | | SCAC4 |
| 47 | MDBF | MCRAE, D & A INC | | | SCAC4 |
| 48 | MDBL | MAD DOG BROKERAGE INC | | | SCAC4 |
| 49 | MDBM | MEDBULK MARITIME | | | SCAC4 |
| 50 | MDBN | MASON AND DIXON LINES | | | SCAC4 |
| 51 | MDBT | MDB TRANSPORTATION | | | SCAC4 |
| 52 | MDBU | MED BOX SL | | | SCAC4 |
| 53 | MDBW | MID-ATLANTIC INTERNATIONAL FREIGHT | | | SCAC4 |
| 54 | MDC | Atlantic Aero, Inc. d/b/a Atlantic Aero And Mid-Atlantic Freight | Callsign: Night Ship, | USA | AVCODES |
| 55 | MDC | Atlantic Aero and Mid-Atlantic Freight | | | ICAO1 |
| 56 | MDCC | MID-COLUMBIA CHARTERS INC | | | SCAC4 |
| 57 | MDCH | MERRITT, DONALD C | | | SCAC4 |
| 58 | MDCL | MACDONALD CARTAGE LTD | | | SCAC4 |
| 59 | MDCN | MID CONTINENT TRUCKING COMPANY | | | SCAC4 |
| 60 | MDCO | MID-ATLANTIC LEASING CORP | | | SCAC4 |
| 61 | MDCR | MIDLAND TERMINAL COMPANY | | | PWRC |
| 62 | MDCR | MIDLAND COURIER SERVICES, INC | | | SCAC1 |
| 63 | MDCU | MEDLOG (SHANGHAI) CO.,LTD. | | PRC | BIC |
| 64 | MDCW | MID-CONTINENT COAL AND COKE | | | SCAC4 |
| 65 | MDCX | Mexicana de Cobre, S.A. de C.V. | added 7/1989; 1/1994-7/2005; eliminated 1/2006 | | NAKINA |
| 66 | MDCX | Middleboro Chemical Industries, Inc. | 4/1970; added 7/1971; eliminated 1/1972 | | NAKINA |
| 67 | MDCX | Middleboro Chemical Industries, Inc. | 4/70; eliminated 1/72 | | NRHS |
| 68 | MDCX | Mexicana de Cobre, S.A. de C.V. | added 7/89; 1/94-7/2000 | | NRHS |
| 69 | MDCX | *MIDDLEBORO CHEMICAL INDUSTRIES, INC. | | | PWRC |
| 70 | MDCX | +MEXICANA DE COBRE SA DE CV [MEXICANA DE ACIDO SULFURICO, SA DE CV] | | | PWRC |
| 71 | MDCX | Mexicana De Cobre de CV | | | RSRV |
| 72 | MDCX | MEXICANA DE COBRE SA DE CV | | | SCAC4 |
| 73 | MDD | MDA Airlines, Joint-Stock Company | Callsign: Donlines, | RUS | AVCODES |
| 74 | MDD | MDLR Airlines Pvt. Ltd. | IATA: 9Y, | IND | AVCODES |
| 75 | MDD | Air Maryland | Callsign: Air Maryland, | USA | AVCODES |
| 76 | MDD | | | USA | TRAFFIC |
| 77 | MDDA | MUEBLES DE DISENO ANDALUCIA | | | SCAC4 |
| 78 | MDDB | MICROBRASS | | | SCAC4 |
| 79 | MDDE | Maryland and Delaware R.R. Co. | added 1/1978; 1/1980; eliminated 10/1987; 1/1994-7/2005; eliminated 10/2009 | | NAKINA |
| 80 | MDDE | Maryland and Delaware R.R. Co. | added 1/78; 1/80; eliminated 10/87; 1/94-7/2000 | | NRHS |
| 81 | MDDE | MARYLAND & DELAWARE RAILROAD CO. | | | PWRC |
| 82 | MDDE | Maryland and Delaware Railroad | | | RSRV |
| 83 | MDDH | M & D TRANSPORTATION LLC | | | SCAC4 |
| 84 | MDDK | MADDOCK, ROGER, TRANSPORTATION | | | SCAC1 |
| 85 | MDDL | MANDERS DIESEL REPAIR INC | | | SCAC4 |
| 86 | MDDM | M & D LLC | | | SCAC4 |
| 87 | MDDN | MADDEN OIL COMPANY | | | SCAC4 |
| 88 | MDDO | METAL DYNAMICS DETROIT LLC | | | SCAC4 |
| 89 | MDDR | MIDLAND DIRECT INC | | | SCAC4 |
| 90 | MDDX | Old Line Holding Co., Inc. | 7/2000; eliminated 10/2004; 7/2005 (not listed) | | NAKINA |
| 91 | MDDX | Old Line Holding Co., Inc. | Jul-00 | | NRHS |
| 92 | MDDX | OLD LINE HOLDINGS COMPANY INC. | | | PWRC |
| 93 | MDDX | Old Line Holding | | | RSRV |
| 94 | MDDY | MITCHELL, D | | | SCAC4 |
| 95 | MDE | Mauritanienne de Transport Aerien | Callsign: Mauri-Trans, | RIM | AVCODES |
| 96 | MDE | Mauritanienne De Transport Aerien | | | ICAO1 |
| 97 | MDE | MANTENIMIENTO DE ESTACIONES, S.L. | | ES | VKM |
| 98 | MDEA | MEDINA TRANSPORTATION | | | SCAC4 |
| 99 | MDEB | MIDNITE EXPRESS INC | | | SCAC4 |
| 100 | MDED | MD ENTERPRISE | | | SCAC4 |
