A study on prevalence and risk factors of Giardia duodenalis infection was conducted in rural communities of Malaysia. A total of 917 individuals between 2-70 years old (431 males and 486 females), participated in this study. The overall prevalence of G. duodenalis infection was 19.2%. The prevalence was significantly different between different age groups, but not genders. Our study indicated that age < or = 12 years old and the presence of family members infected with G. duodenalis were the risk factors of infection. Person-to-person contact within the family members was the possible mode of transmission. Health education on personal hygiene, together with the treatment of the infected people, may help in reducing and controlling this infection in these communities.