Twenty-one patients with adrenocortical carcinoma (ACC) diagnosed at three hospitals over a ten-year period were reviewed for clinical and pathologic features that might have therapeutic implications. Depending upon the extent of cellular pleomorphism, ACC could be defined as anaplastic or differentiated. Anaplastic ACC occurred more often in male patients, produced more frequent cutaneous metastases (P = 0.01), and was associated with a lack of clinical or laboratory evidence of hormone production (P = 0.01). In contrast, differentiated ACC usually occurred in women and produced clinical or laboratory evidence of hormonal excess. Median survival time of patients with anaplastic ACC was only five months, while median survival time of those with differentiated ACC was 40 months (P = 0.005). Patients with differentiated ACC survived for long periods, even with metastatic disease. Three of 5 such patients had objective responses to o,p'-DDD (Mitotane) therapy. The histopathology of ACC is an important prognostic factor and should be considered in the design of future therapeutic trials.