&NA;A 21‐year‐old man with an oligodendroglioma in the anterior horn of the right lateral ventricle complained of sexual dysfunction and showed lowered concentrations of serum testosterone (1.1 ng/ml) with normal pituitary function. Human chorionic gonadotropin testing revealed a good testosterone response (1.1 to 4.9 ng/ml) and a clomiphene test revealed no gonadotropin response. Pulsatile secretion of luteinizing hormone (LH) was absent preoperatively. After removal of the tumor, serum concentration of testosterone increased to the normal range, LH pulsatility appeared, and the patient had no complaints of sexual dysfunction. In this patient, the loss of LH pulsatility responsible for his hypogonadism was caused by the lateral ventricle tumor compressing the surrounding structures, and this was corrected by tumor resection. (Neurosurgery25:820‐823, 1989)