A histologic study of 15 ovaries from patients in whom endometrial adenocarcinoma developed before the age of 40 years was performed. These ovaries were randomized with control groups of 21 age-matched normal ovaries and 25 ovaries from patients who had Stein-Leventhal syndrome. The study was done in an attempt to determine whether the ovaries from these young patients showed any histologic feature that would indicate abnormal ovarian function resulting in unopposed estrogenic stimulation of the endometrium. Histologic features assessed included type and size of cysts, presence and number of primary follicles, corpora lutea, corpora albicantia, and presence of stromal luteinization and sclerosis. Analysis of the results indicated that from a histologic point of view ovaries of patients less than 40 years old who have endometrial adenocarcinoma are more similar to normal ovaries than to polycystic ovaries. Only 11.1% of ovaries of the study group had features suggestive of polycystic ovarian disease.