Mitotane is considered to be the drug of choice for patients with inoperable, recurrent and metastatic adrenocortical carcinoma, although a favourable effect of this drug on survival has never been documented. We evaluated the efficacy of mitotane treatment of 96 patients with adrenocortical carcinoma followed up in our department between 1959 and 1992. Complete tumour resection was the goal of the initial treatment. Mitotane treatment was classified according to serum trough concentrations on maintenance therapy: low (< 14 mg l-1) or high (> or = 14 mg l-1). Total tumour resection was feasible in 47 patients (49%), and subtotal resection was performed in 37 patients (39%). Patients who underwent total tumour resection survived significantly longer than those who did not (P < 0.001). Adjuvant mitotane therapy (n = 11) did not influence survival after total resection. Sixty-two patients were given mitotane treatment at some time during their illness, only 30 of whom reached high maintenance serum levels. Mitotane treatment with high serum levels had an independently favourable influence on patient survival, using univariate (P < 0.01) and multivariate analysis (P = 0.01). Mitotane treatment resulting in low serum levels was tantamount to not giving mitotane at all. We conclude that mitotane treatment in adrenocortical carcinoma is effective only when high serum levels can be achieved.