A case of open carpo-metacarpal dislocation complicated by dislocation of the os trapesium is reported in this paper. The patient's wrist healed with good functional results, despite a partial mistake in diagnosis. The authors draw attention to the fact, that X-ray films taken at admission must be analysed carefully and intraoperative X-rays films must be taken. By demonstration their own mistake in diagnosis and treatment, the authors hope that a similar mistake will be avoided. Following early open or closed reduction, a temporary wire fixation of the metacarpal bones to the carpal bones is recommended in order to prevent redislocation.