The purpose of this study was to investigate the association of stress fractures with age, sex, sport level, sporting activity, and skeletal site in athletes seen at our sports medicine clinic between September 1991 and May 2001. During these 10 years, 10 726 patients (6415 males, 3861 females) visited our clinic because of sport-related injuries, and 196 patients [125 males (1.9%), 71 females (1.8%)] sustained stress fractures. The average age of the patients with stress fractures was 20.1 years (range 10-46 years); 84 patients (42.6%) were 15-19 years of age, and 68 (34.7%) were 20-24 years of age. Altogether, 74 patients (37.8%) were active at the high recreational level and 122 (62.2%) at the competitive level. The sites of the stress fractures varied from sport to sport. The ulnar olecranon was the most common stress fracture site among baseball athletes and the rib among the rowing athletes. Classical ballet, aerobics, tennis, and volleyball athletes predominantly sustained stress fractures of the tibial shaft. Basketball athletes predominantly sustained stress fractures of the tibial shaft and medial malleolus and the metatarsal bone, whereas track and field and soccer athletes predominantly sustained stress fractures of the tibial shaft and pubic bone. Our results show that stress fractures are seen even in high-level adolescent athletes, with similar proportions for males and females, and that particular sports are associated with specific sites for stress fractures.