The levels of cardiovascular risk factors vary in different segments of a population. Our aim was to investigate ethnic differences in cardiovascular risk factors among five major immigrant groups in Oslo, Norway. A population-based, cross-sectional study. The Oslo Immigrant Health study was conducted in 2002. All first-generation immigrants aged 31-60 years living in Oslo from Sri Lanka, Turkey, Iran, Vietnam, and a random sample of 30% of those from Pakistan, were invited. A total of 3019 individuals provided written consent and met the inclusion criteria. Participants had a clinical examination, blood test, and were asked to complete the study questionnaire. Immigrants from Vietnam had the highest high-density lipoprotein (HDL) cholesterol, whereas immigrants from Sri Lanka and Pakistan, and men from Turkey, had the lowest HDL-cholesterol and highest triglycerides. Immigrants from Sri Lanka, Pakistan and Turkey had the highest blood pressure. Smoking was least prevalent among Sri Lankan immigrants and most common among Turkish immigrants. Ethnic differences in blood pressure and HDL-cholesterol, and triglycerides among women, were attenuated after adjusting for obesity measures. A moderate and higher (> or =10%) Framingham risk score was most common among Turkish and Pakistani immigrants. We found ethnic differences in triglycerides, HDL-cholesterol and blood pressure; however, the differences in blood pressure were surprisingly small. Ethnic differences were partly explained by obesity. The prevalence of smoking also varied greatly between the different ethnic groups.