The epidemiological features and clinical manifestations of adult cases of brucellosis admitted to the Department of Infectious Diseases, Babol Medical University, Iran from 1997 to 2002 were investigated. Of 469 cases, 267 (56·9%) were males. The mean age of cases was 36·9±15 years. Most (60·8%) were from rural areas. Two thirds of cases (306, 66·3%) presented during spring or summer. Fresh cheese (22·4%), animal husbandry (11·3%), laboratory worker (8·1%) and veterinary profession (1·5%) were the main risk factors. Forty-five families (9·6%) had two cases. Sweating, fever, and arthralgia were the most frequent clinical symptoms. Complications were documented in 105 males (39·5%) and 41 females (20·3%, P=0·0001). Peripheral arthritis was seen in 24 (9%) males and 19 (9·4%) females, with knees and hips being the most common sites of infection. Sacroiliitis and spondylitis were seen in 28 (6%) and 32 (6·8%) cases respectively with spondylitis more common in males (P=0·023). Epididymo-orchitis was seen in 29 (10·9%) males. There were three cases each of endocarditis (0·6%) and neurological complications (0·6%). Most patients with brucellosis did not have any of the known risk factors for brucellosis. Thus consumption of unsafe dairy products could be the main route of infection. The disease manifested with a diversity of clinical manifestations and complications. Complications were more frequent in males than females.