Apophysitis describes a chronic traction injury at the insertion site of a tendon. There is a gradual onset of pain with no clear history of injury. Without adequate preventive methods, an avulsion fracture may result. The case is here reported of an apophyseal avulsion fracture of the anterior superior iliac spine in an adolescent caused by playing football before the end of treatment for apophysitis. An open reduction and internal fixation was performed followed by a rehabilitation programme. No complications occurred, and the patient had returned to his previous level of sporting activity after six weeks.