OBJECTIVE: To estimate the distribution of blood pressure (BP), body mass index (BMI), smoking habits and their associations with socioeconomic status (SES) in an urban population in early epidemiological transition. METHODS: Cross-sectional survey of the entire population aged 25-64 years in five branches of Dar es Salaam (Tanzania) through visits to all homes in the study area. Blood pressure was based on the mean of the second and third readings with an automated device. Socioeconomic status was estimated with indicators of education, occupation and wealth. RESULTS: In all 9254 people were examined. Age-adjusted prevalence (%) among men/ women aged 35-64 years was 27.1/30.2 for BP > or = 140/90 mmHg or antihypertensive medication, 13.1/17.7 for BP > or = 160/95 mmHg or antihypertensive medication, 28.0/27.4 for BMI of 25.0-29.9 kg/m(2), 6.9/17.4 for BMI > or = 30 kg/m(2), and 22.0/2.6 for smoking (> or = 1 cigarette per day). Prevalence of categories of drinking frequency and history of diabetes are also reported. After adjustment for covariates, SES was associated inversely with BP and smoking and directly with BMI. Body mass index was associated positively with BP (1.01 and 0.91 mmHg systolic BP per 1 kg/m(2) BMI in men and women, respectively) and inversely with smoking (-1.14 kg/m(2) in male smokers versus non-smokers). Hypertension treatment rates were low, particularly in people of low SES. CONCLUSIONS: High prevalence of several cardiovascular risk factors in the urban population of a low-income country stresses the need for early public health interventions and adaptation of the health care infrastructure to meet the emerging challenge of cardiovascular disease. The direct SES-BMI association may drive increasing BMI and BP while the population becomes more affluent.