In a study of 194 masculinizing ovarian tumors from the Ovarian Tumor Registry, the criteria for reclassifying these tumors on a histologic basis are discussed. It is proposed that the terms "gynandroblastoma" and "arrhenoblastoma" be discarded in favor of "gonadal stromal," and that the general classification of "lipoid tumor" can be avoided if careful search is made for specific histologic structures. Finally, it is suggested that the malignancy rate for gonadal stromal tumors, Sertoli-Leydig tumors, hilus cell tumors and adrenal rest tumors is closer to 5% rather than 25-30%.