Objective: To document body composition and fat patterning characteristics in normal and underweight infertile women. Design: Status quo method. Setting: University clinics. Patient(s): Fifteen amenorrheic women with anorexia nervosa, 16 women with polycystic ovary syndrome (PCO2), 10 women with primary amenorrhea and 19 healthy controls. Intervention(s): None. Main Outcome Measure(s): Determination of body mass index, body composition parameters such as fat mass, lean body mass, bone mass using dual-energy x-ray absorptiometry (DEXA), fat distribution patterns, 17beta-estradiol, FSH, LH, prolactin, progesterone, testosterone, DHEA-S, and androstenedione levels. Result(s): A statistically significant difference was found comparing all proband groups with healthy controls for the majority of body fat and bone mineral content parameters but not for lean body mass. Infertile women of normal weight, with PCOS, and with primary amenorrhea exhibited an extraordinarily high amount of fat tissue and a tendency toward android fat patterning. In contrast, patients with anorexia nervosa and the healthy controls showed predominantly gynoid fat patterning. According to logistic regression analyses, anorexia nervosa was characterized by reduced fat tissue and PCOS was characterized by android fat patterning and an increased fat percentage. Patients with primary amenorrhea were characterized by reduced bone mass. Conclusion(s): Infertile young women showed characteristic differences in body composition and fat distribution patterns when compared with healthy, fertile, age-matched counterparts.