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 > 20 mitoses per 50 high power fields (hpf) had a median survival of 14 months, whereas the 21 patients with carcinomas with ≤ 20 mitoses had a median survival of 58 months (p < 0.02). The presence of atypical mitoses, capsular invasion, tumor weight > 250 g, and size > 10 cm each showed a marginal statistical association with poor survival (p < 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 >20 mitoses be designated high grade, whereas tumors with ≤20 mitoses be designated low grade.