Seventy-two children who ingested thallium-sulphate-containing pesticides between 1954 and 1959 were followed up from 6 months to 7 years to determine the long-term consequences. Thallium sulphate poisoning was responsible for the deaths of 9 of the 72 children, and for persistent neurological damage in 26. The clinical features of the acute stage were correlated with the follow-up status to evaluate which features may aid in judging prognosis. Gastrointestinal disturbances, cardiovascular abnormalities, coma, convulsions, and mental aberration were found to be prognostically unfavorable. An analysis of the various forms of antidote therapy revealed that they were apparently no more effective than symptomatic treatment.