HeIicobacter pylori infection rate was determined in 697 consecutive patients with ulcer, gastritis, duodenitis and non-ulcer dyspepsia by endoscopy at a Malaysian hospital in 1999-2002. Biopsies of the gastric antrum and body were subjected to the urease test, Gram staining of impression smears and culture examination. Infection was defined as a positive result in at least one test. The infection rates were 32.1, 10.4, 20.0 and 16.2% in ulcer, gastritis, duodenitis and non-ulcer dyspepsia patients, respectively. Overall, the prevalence of H. pylori infection was 14.6%, with the rate among the Indian (21.7%), Chinese (19.2%) and Bangladeshi foreign worker (23.1%) groups significantly higher (P<0.05) than that of the Malays (5.8%). Generally, the prevalence rate among males (18.9%) was significantly higher (P<0.001) than that among females (9.0%), but for a particular ethnic group, such trend and significant differences (P<0.05) were observed only among the Malays. In terms of gender, the prevalence rates of Malay males and females were also significantly lower (P<0.05) than those of Chinese and Indians. In conclusion, there is a significant difference in H. pylori infection prevalence rates among ethnic groups (highest in Indians, then Chinese and unusually low in Malays) and gender groups (highest in males) in Malaysia.