In this paper we document seventy fractures of the humeral shaft that were treated by intramedullary fixation between 1970 and 1981. Complications developed in forty-seven (67 per cent) of the fractures, and forty-five (64 per cent) required at least one additional operative procedure. Of the sixty fractures that were internally fixed within six weeks after injury, nine (15 per cent) had a delayed union and five (8.3 per cent) had a non-union, two of which persisted despite subsequent surgery. Three of the ten fractures that were internally fixed more than six weeks after injury never united despite additional procedures that were done to secure union. Delayed union and non-union were more common in open fractures (33 per cent) than in closed fractures (21 per cent), and with open reduction (39 per cent) than with closed or so-called semi-open reduction (9 per cent). Deep infection occurred in three (5 per cent) of the fractures and was more common in open (17 per cent) than in closed fractures (2 per cent). One of the three open fractures that were treated by immediate fixation became infected, as compared with only one of the nine open fractures treated by delayed fixation. Painful adhesive capsulitis of the shoulder developed in thirty-four (56 per cent) of the patients who had fractures treated with distally directed pins, but motion of the elbow was not restricted in the nine patients with fractures treated with proximally directed pins.