Seventeen granulosa cell, thirteen Sertoli-Leydig cell and six unclassified sex cord-stromal tumors diagnosed during pregnancy or the puerperium were reviewed. Eleven patients presented with abdominal pain or swelling, five in shock, two with virilization, and one with vaginal bleeding. Three asymptomatic patients were explored because of a palpable mass and one because of an adnexal mass found on ultrasound examination. In thirteen patients the tumor was discovered during a cesarean section; five of them had had dystocia and in eight of them the tumor was an incidental finding. All the tumors were Stage I but 13 of them had ruptured; all but one were unilateral. Hemoperitoneum was present in seven cases. On microscopical examination many of the tumors differed from tumors in the same diagnostic categories occurring in the absence of pregnancy by having a disorderly arrangement of their cells, lacking recognizable differentiation in many areas, showing prominent edema, and containing unusually large numbers of lutein or Leydig cells. The last two features were most obtrusive in tumors removed at term. With one exception the patients were initially treated by conservative surgical procedures. Two of them received chemotherapy and two radiation therapy postoperatively. A hysterectomy and salpingo-oophorectomy was performed at a second operation in eight cases; no residual tumor was found in any of the specimens. Only one patient had a recurrence, which was treated surgically. Follow-up for an average of 4.7 years is available for 30 of the 36 patients; all of them were alive and free of disease at the time of the last examination.