An industrial accident in Seveso, Italy, in 1976, caused contamination of the residential community with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We investigated cancer occurrence in the first post-accident decade (1977-1986) among nearly 20,000 subjects aged 0-19 years. People who left the area were actively followed with a 99% follow-up rate. For reported cancer cases confirmation was obtained through consultation with original medical records. Two ovarian cancers were observed versus none expected. A suggestive increase was seen for Hodgkin's lymphoma (relative risk [RR] = 2.0; 95% confidence interval [CI] = 0.5-7.6). Myeloid leukaemia showed a clear, but not statistically significant increase (RR = 2.7; 95% CI = 0.7-11.4). The most prominent result concerned thyroid cancer, not just for the magnitude of the increase (two cases, RR = 4.6; 95% CI = 0.6-32.7), but also for its consistency with experimental findings and previous observations in humans. Any conclusive interpretation would be premature because of the short time since initial exposure, ecological definition of exposure status, and limited number of events.