BACKGROUND: Rare cancers are a challenge to clinical practice, and treatment experience, even in major cancer centres to which rare cancers are usually referred, is often limited. We aimed to study the epidemiology of rare cancers in a large population of several countries. METHODS: We analysed survival by age, sex, subsite, and morphology in 57,144 adults with 14 selected rare cancers diagnosed 1983-94. Variations in survival over time and between European regions were also assessed for variations in quality of care. We also estimated the adjusted relative excess risk of death for every rare cancer. FINDINGS: Overall 5-year relative survival was good (ie, >65%) for placental choriocarcinoma (85.4% [95% CI 81.4-89.5]), thyroid medullary carcinoma (72.4% [69.2-75.5]), ovarian germ-cell cancer (73.0% [70.0-76.0]), lung carcinoid (70.1% [67.3-72.9]), and cervical adenocarcinoma (65.5% [64.3-66.6]); intermediate (ie, 35-65%) for testicular cancer at age 65 years or older (64.0% [59.3-68.7]), sarcoma of extremities (60.0% [58.9-61.2]), digestive-system endocrine cancers (55.6% [54.9-56.3]), anal squamous-cell carcinoma (53.1% [51.5-54.8]), and uterine sarcoma (43.5% [42.0-44.9]); low for carcinoma of adrenal-gland cortex (32.7% [28.3-37.2]) and bladder squamous-cell carcinoma (20.4% [18.8-22.0]); and poor for angiosarcoma of liver (6.4% [1.8-11.0]) and mesothelioma (4.7% [4.3-5.2]). Survival was usually better for women than men and poor in those aged 75 years or older. Survival significantly improved over time for ovarian germ-cell cancer, sarcomas of extremities, digestive-system endocrine tumours, anal squamous-cell carcinoma, and angiosarcoma of liver. Survival in northern Europe was higher than in the other geographic groupings for most cancers. INTERPRETATION: Because effective treatments are available for several of the rare cancers we assessed, further research is needed to ascertain why survival is lower in some European countries than in others, particularly in older patients. Audit of best practice for rare cancers with treatment protocols would be useful.