BACKGROUND: There is controversy over whether patients presenting with a primary attack of acute diverticulitis at a younger age are more prone to complications and recurrence than older patients. METHODS: A review, including postal questionnaires, was undertaken of 234 patients who had a primary episode of acute diverticulitis. The diagnosis was confirmed by computed tomography (CT) and/or pathology report. The mean length of follow-up was 30 (range 16-45) months. RESULTS: In 58 patients aged 50 years or less no differences in fever or white blood cell count were found in comparison with findings in 176 patients aged above 50 years. The rate of severe diverticulitis observed with CT was lower in the younger patients (2 versus 11.9 per cent; P = 0.025). Surgical management during the first admission was undertaken less commonly in younger patients (2 versus 6.8 per cent; P = 0.271). Rates of subsequent events (recurrent diverticulitis and/or further surgery) during follow-up were higher in younger patients (25 versus 19.5 per cent), but this was not significant (P = 0.423). A type II error cannot be excluded. CONCLUSION: First episodes of acute diverticulitis were not more aggressive in patients aged 50 years or less. Recurrence rates were slightly higher than in older patients. 2008 British Journal of Surgery Society Ltd. Published by John Wiley & Sons, Ltd.