Data are presented on the occurrence of chloracne, clinical symptoms and biochemical changes in 164 children following environmental contamination by TCDD from an industrial accident in Seveso, Italy. An overall positive association was found between the territorial distribution of chloracne cases and the different levels of soil contamination in the affected area. Individual risk factors such as condition and length of exposure, intake via contaminated foods, etc. were evaluated; no single factor appeared to be associated with chloracne. Disturbances of the gastrointestinal tract were more frequently observed in children affected with chloracne in those from the same areas having no skin lesions. However, no clinically definable systemic disease has been diagnosed.