Forty-one patients with pure immature teratoma of the ovary treated at The University of Texas M. D. Anderson Hospital and Tumor Institute at Houston from 1944 to 1985 were reviewed. The median age of these patients was 17 years. The most common symptom was abdominal pain, which occurred in 39 (95%) patients. FIGO stages included 24 patients with stage I, four with stage II, 12 with stage III, and one stage IV. The tumors ranged in size from 6 to 31 cm in greatest diameter, with a median of 17 cm. Of 39 cases reexamined microscopically, four were grade 1 tumors, 22 were grade 2 tumors, and 13 were grade 3 tumors. Initial surgery included ovarian cystectomy in one patient, unilateral salpingo-oophorectomy in 27 patients, and bilateral salpingo-oophorectomy in 13 patients. Fifteen of 16 patients treated with surgery alone developed recurrent disease; 11 are surviving after further therapy. Two patients died after treatment with radiotherapy plus chemotherapy. Twenty-one patients received a combination of vincristine, actinomycin-D, and cyclophosphamide postoperatively, and 18 are alive and well. One of two patients who received other combination regimens is alive and well. Therefore, 29 of the 41 patients (71%) are alive and well. Optimal management of patients with pure immature teratoma of the ovary consists of initial surgery (with preservation of a normal contralateral ovary in most patients) followed by combination chemotherapy in all patients except those with stage I, grade 1 disease; the latter may be treated safely with surgery alone.