Young individuals have a high recurrence rate following non-operative treatment of traumatic primary anterior shoulder dislocation. The present multicentre study was undertaken to find out whether the results could be improved by using arthroscopic lavage as treatment. Sixty patients aged 16-30 years, with traumatic primary anterior shoulder dislocation were randomised into two groups. One group was treated with arthroscopic lavage within 10 days, while the other group was treated non-operatively. Rehabilitation was otherwise identical. At 1-year follow-up, 4 of 30 patients (13%) in the lavage group had had redislocation compared with 13 of 30 (43%) in the group treated non-operatively (P = 0.01). The difference in recurrence rate was more pronounced in younger patients. The functional outcome according to the Rowe shoulder score was better in the lavage group (P = 0.003), as was the anterior stability according to the apprehension test (P = 0.008). We conclude that arthroscopic lavage reduced the recurrence rate and produced a better functional outcome at 1-year follow-up than the non-operative treatment in young individuals.