Approximately 10% of gonadal stromal (sex cord-stromal) tumors of the ovary are difficult to classify. In most of these cases, the differential diagnosis is between granulosa and Sertoli-Leydig types. We studied 32 such neoplasms. The tumors were divided into two groups: Group 1 consisted of tumors with a predominance of a primitive spindle-cell stroma without specific differentiation, and group 2 consisted of tumors with a predominance of cords, trabecula, or tubules with features suggestive of or characteristics of both granulosa and Sertoli-Leydig cell differentiation in different areas. All tumors had overall features that did not permit definitive placement into granulosa or Sertoli-Leydig categories. There were 18 group 1 tumors and 14 group 2 tumors. The mean patient age was 49 years. The International Federation of Gynecology and Obstetrics (FIGO) stage was known in 12 patients, all of whom were in stage I. Survival data were available for 17 patients, whose follow-up was a mean of 8 years of until death. There were three deaths, one of which was of unrelated causes. the 5- and 10-year corrected actuarial survival rates were 92% and 74%. The number of patients was too small to make meaningful comparisons between the two groups. We concluded that the behavior of these unclassified tumors is similar to that of granulosa and Sertoli-Leydig tumors, with a favorable prognosis when confined to the ovaries.