One hundred fifteen patients with inoperable adrenal cortical carcinoma were treated with mitotane (o,p' = DDD). Eighty-five percent of the patients with elevated urinary steroid levels showed a marked reduction, 61% of the patients whose conditions we were able to evaluate showed a measurable disease response, and 45% showed an overall clinical response. These results are all markedly better than those described in earlier reports. In previous reports earlier recognition of the disease and institution of chemotherapy with mitotane resulted in the improvements described. There was no evidence of serious organ poisoning, except for the effects upon the adrenal cortex. On the basis of these data, early diagnosis and treatment of inoperable adrenal cortical carcinoma with mitotane seem to be useful.