A clinical description of luteinized unruptured follicles is presented. This abnormality in ovulation is characterized by normal endocrinologic presumptive signs of ovulation: biphasic basal body temperature curves, secretory endometrium, and laboratory evidence of progesterone production by elevated urinary pregnanediol or plasma progesterone levels. In a group of 102 such infertile women, laparoscopy performed 3 to 5 days after apparent ovulation revealed the absence of a corpus hemorrhagicum in 30 women, and the absence of a sigma on a corpus hemorrhagicum in an additional 32 women. These findings were evidence that a follicle had not ruptured and an ovum had not escaped. Of 28 patients undergoing follicular stimulation with clomiphene citrate or human menopausal gonadotropin after this diagnosis, 15 conceived.