BACKGROUND: Diagnosis of acute abdominal pain in older persons is a challenge, with the age-related increase in concurrent diseases. In most western countries the number of elderly people is constantly rising, which means that an increasing proportion of patients admitted for abdominal pain at the emergency department are elderly. OBJECTIVE: To characterize differences in clinical presentation and diagnostic accuracy between younger and more elderly patients with acute abdominal pain. METHODS: Patients admitted to Mora Hospital with abdominal pain of up to seven days' duration were registered according to a detailed schedule. From 1st February 1997 to 1st June 2000, 557 patients aged 65-79 years and 274 patients aged > or = 80 years were registered. Patients aged 20-64 years (n = 1,458) served as a control group. RESULTS: A specific diagnosis, i.e. other than 'nonspecific abdominal pain', was established in 76 and 78% of the patients aged 65-79 and > or = 80 years respectively, and in 64% of those aged 20-64 (p or = 65 years. Rebound tenderness (p or = 65 years, C-reactive protein did not differ between patients operated on and those not, contrary to the finding in patients