Four patients were referred to the Royal National Orthopaedic Hospital with iatrogenic accessory nerve palsy because their symptoms were severe enough to warrant surgical treatment. The definitive diagnosis was made several months after the initial procedure, when wasting of the trapezius and shoulder dysfunction became apparent. The reasons for this delay are discussed along with prophylaxis and surgical technique of treatment. Less significant degrees of paralysis manifest themselves on return to activity in which the hands are required to be above shoulder level. Electromyograms in these cases will confirm the diagnosis (1).