This survey presents epidemiological, serological and clinical features of 270 patients (85% males, 18% children) treated for leptospirosis from 1969 to 2003 at the Clinic for Infective Diseases, University Hospital Osijek, Osijek, eastern Croatia. 75% of the admissions were between July and October. The route of transmission was mostly by indirect contact with domestic animals, less frequently by direct contact with urine or tissue of infected animals. Clinical presentation included signs and symptoms with expected and common frequency, with the exception of jaundice (62%) and aseptic meningitis (60%), which occurred with higher incidence than previously reported. Acute renal failure ensued in 53% of patients, 7% of whom required haemodialysis. No deaths were observed. Therapy consisted of antimicrobials (penicillin and doxycycline) and symptomatic measures. Diagnosis was confirmed by microscopic agglutination test (MAT). There were in total 18 serological types of Leptospira detected, and types L. sejroe, L.pomona, L. australis and L. icterohaemorrhagiae prevailed. During the last 10 y some new types were observed. Leptospirosis was not rare in the region of eastern Croatia, and its course could be life-threatening if not recognized and adequately treated.