A case of acute arsenical intoxication arising from ingested well water containing only 1.2 ppm of arsenic is reported. After a latent period of 14 years, multiple cutaneous basal cell carcinomas developed. The water was analyzed for a variety of other trace elements and compounds and no evidence for the existence of other carcinogens was found. This study strengthens the concept that arsenic is a carcinogen. The role of a possible selenium deficiency is also discussed.