The clinical and pathological features of 125 juvenile granulosa cell tumors of the ovary were analyzed. The patients ranged in age from newborn to 67 years (average 13 years). Forty-four percent were 10 years of age or younger, 34% between 11 and 20 years, 18% between 21 and 30 years, and 3% over 30 years of age. Eighty-two percent of the prepubertal patients presented because of isosexual pseudoprecocity. In the remainder of the children and in most of the older patients, the presenting manifestation was usually abdominal pain or swelling. Fifteen patients in the reproductive age group had menstrual irregularities or amenorrhea, and one of the two postmenopausal women presented with uterine bleeding. Two patients had Ollier's disease and two had Maffucci's syndrome. Laparotomy revealed unilateral involvement in 122 cases and involvement of both ovaries in two cases; bilateral tumors were found at autopsy in one case. Two tumors were Stage IIb and one Stage IIc; the remainder were Stage I. In 13 cases (11%), rupture had occurred before or during operation and ascites was present in 11 cases (9%). The tumors ranged from 3 to 32 cm in diameter (average 12.5 cm). Forty-nine percent of them were solid and cystic, 37% solid, and 14% cystic. Microscopic examination disclosed diffuse and follicular patterns, with the former predominating in most of the cases. The follicles varied in size and shape and characteristically contained basophilic or eosinophilic secretion, which often stained positively for mucin. The granulosa cells were typically luteinized to varying degrees and had dark round nuclei without grooves; a theca cell component of variable extent was present in many of the cases. The mitotic rate ranged from less than 1 to 32/10 high-power fields, with an average of 7. Nuclear atypicality varied from Grade 1 to 4. Follow-up information of at least 1 year's and up to 21 years' (average 5 years') duration was available for 95 patients, 87 of whom (92%) were alive and free of disease. One patient with Maffucci's syndrome died of chondrosarcoma 11 years after removal of the ovarian tumor (corrected survival--93%). The seven remaining patients died as a result of their tumor from 7 months to 3 years postoperatively; one of the clinically malignant tumors was Stage Iai, one Stage Iaii, two Stage Ic, two Stage IIb, and one Stage IIc.(ABSTRACT TRUNCATED AT 400 WORDS)