Two sisters, ages 16 and 17, presented with secondary amenorrhea. In addition, primary ovarian failure, gonadal dysgenesis, and normal karyotypes were demonstrated. The most significant finding was a history of mumps, which they caught at the same time, 10 years before the onset of the amenorrhea. This disorder suggests that etiologic and environmental factors could prevail either in utero or during childhood. These patients are presented to emphasize the importance of considering gonadal dysgenesis as a differential diagnosis in patients with secondary amenorrhea, especially when the menstrual life has been a short one.