The clinical and pathological features of 63 steroid cell tumors, not otherwise specified, were reviewed. The patients ranged in age from 2 1/2 to 80 years. The most common initial manifestation was virilization (41%); four patients had estrogenic manifestations, and four had hypercortisolemia with Cushing's syndrome. The tumors, 6% of which were bilateral, ranged from 1.2 to 45 cm in greatest dimension. Microscopic examination revealed two types of cells, which had overlapping features: those with abundant eosinophilic cytoplasm and those with vacuolated cytoplasm. Fat stains were positive in 75% of the 16 cases in which they were performed. Follow-up data ranging from 1 to 19 years (average 5.2 years) in duration were available for 50 patients. In 24 cases, the tumor was designated probably benign (no evidence of spread beyond the ovary within 3 or more years postoperatively). In 18 patients, the tumor was clinically malignant. The best pathological correlates of malignant behavior were: the presence of two or more mitotic figures per 10 high power fields (92% malignant); necrosis (86% malignant); a diameter of 7 cm or greater (78% malignant); hemorrhage (77% malignant); and grade 2 or 3 nuclear atypia (64% malignant).