The microbial aetiology of genital ulcers was studied in 249 patients (241 men and 8 women) attending a Sexually Transmitted Disease Clinic in Kuala Lumpur, Malaysia. Herpes simplex virus type 2 was isolated in 48 (19.2%) patients, Haemophilus ducreyi from 22 (8.8%), Neisseria gonorrhoeae from seven (2.8%) and Chlamydia trachomatis from four (1.6%). Syphilis was diagnosed in 18 (7.2%) patients on the basis of dark field microscopy. Two (0.8%) patients were found to have both chancroid and syphilis and one (0.5%) had both gonorrhoea and syphilis. No organism was isolated in the remaining 151 (61.5%) patients. Overall, the accuracy of clinical diagnosis was 58% for single infection, 67% for herpes, 63% for syphilis, 47% for chancroid and 0% for lymphogranuloma venereum. Therefore, our study confirms the need for laboratory tests to diagnose accurately the aetiology of genital ulcer disease.