As a member of the American Thoracic Society you may join a maximum of three assemblies one “primary Assembly” and two “secondary Assembly's”. As of July 9, 2026, 14,661 have declared a primary Assembly.
| Assembly | Primary Members | Secondary Members | Primary & Secondary Members | Primary & Secondary (U.S. Only) | Primary (U.S. Only) | International Members | Percentage of International Members |
| Allergy, Immunology and Inflammation (AII) | 1248 | 1953 | 3201 | 1935 | 776 | 1266 | 40% |
| Behavioral Science & Health Services Research (BSHSR) | 445 | 766 | 1211 | 994 | 378 | 217 | 18% |
| Clinical Problems (CP) | 2333 | 2846 | 5179 | 3587 | 1545 | 1592 | 31% |
| Critical Care (CC) | 3594 | 2928 | 6522 | 5358 | 3089 | 1164 | 18% |
| Environmental, Occupational and Population Health (EOPH) | 490 | 826 | 1316 | 936 | 361 | 380 | 39% |
| Nursing (NUR) | 108 | 62 | 170 | 146 | 96 | 24 | 14% |
| Pediatrics (PEDS) | 1258 | 459 | 1717 | 1318 | 979 | 393 | 23% |
| Pulmonary Circulation (PC) | 872 | 1439 | 2311 | 1821 | 684 | 490 | 21% |
| Pulmonary Infections and Tuberculosis (Pi-TB) | 940 | 1903 | 2843 | 1658 | 461 | 1185 | 42% |
| Pulmonary Rehabilitation (PR) | 246 | 548 | 794 | 401 | 113 | 393 | 49% |
| Respiratory Cell and Molecular Biology (RCMB) | 933 | 1330 | 2263 | 1617 | 691 | 646 | 29% |
| Respiratory Structure and Function (RSF) | 778 | 1878 | 2656 | 1862 | 481 | 794 | 30% |
| Sleep and Respiratory Neurobiology (SRN) | 626 | 895 | 1521 | 929 | 390 | 592 | 39% |
| Thoracic Oncology | 790 | 816 | 1606 | 1082 | 556 | 524 | 33% |
| Genetics & Genomics (GG) | 1063 | ||||||
| Medical Education (Med Ed) | 2728 | ||||||
| Terrorism & Inhalation Disasters (TID) | 327 | ||||||