We report a case of a 21-year-old male with massive hypertrophic ischial tuberosity non-union. Among multiple other lesions, the patient suffered an open avulsion of the ischial tuberosity in a severe traffic accident in adolescence. A conservative treatment was decided for the avulsion. Because of sciatic pain and difficulties while sitting since the age of 19, X-rays were realised and showed a massive hypertrophic non-union of the ischial tuberosity. To preserve hamstring origin with bone attachment, the non-union was mobilised, reduced by osteotomy and fixed by plate and screws. At the follow up of one year, the patient sits without pain and can work without interruption. Avulsion of the ischial tuberosity is infrequent and the diagnosis is often missed (Gidwani et al., BMJ 329:99–100, 2004; Hamada, Clin Orthop 31:117–130, 1963). This lesion is more often seen in adolescence as the consequence of a sport injury (Gidwani et al., BMJ 329:99–100, 2004). Treatment is generally conservative and outcome good. Surgical therapy is only needed in cases with severe displacement. Long-term problems are seldom and surgical therapy to solve these problems is the exception.