There are currently no well-established pathologic prognostic factors helpful in distinguishing low versus high grade adrenocortical carcinomas. The effect of 11 pathologic parameters on survival was investigated in 42 cases of adrenocortical carcinoma. Only one variable, mitotic rate, had a strong statistical association with patient outcome. The 21 patients with carcinomas with greater than 20 mitoses per 50 high power fields (hpf) had a median survival of 14 months, whereas the 21 patients with carcinomas with less than or equal to 20 mitoses had a median survival of 58 months (p less than 0.02). The presence of atypical mitoses, capsular invasion, tumor weight greater than 250 g, and size greater than 10 cm each showed a marginal statistical association with poor survival (p less than 0.06), whereas other features assessed, such as nuclear grade, presence of necrosis or of venous or sinusoidal invasion, character of the tumor cell cytoplasm, or architectural pattern, showed no statistical significance in predicting survival. It is proposed that adrenal cortical carcinomas with greater than 20 mitoses be designated high grade, whereas tumors with less than or equal to 20 mitoses be designated low grade.