BACKGROUND: There are no methodologically rigorous studies of the incidence of stroke in sub-Saharan Africa. We aimed to provide reliable data on the incidence of stroke in rural and urban Tanzania. METHODS: The Tanzania Stroke Incidence Project (TSIP) recorded stroke incidence in two well defined demographic surveillance sites (DSS) over a 3-year period from June, 2003. The Hai DSS (population 159,814) is rural and the Dar-es-Salaam DSS (population 56,517) is urban. Patients with stroke were identified by use of a system of community-based investigators and liaison with local hospital and medical centre staff. Patients who died from stroke before recruitment into the TSIP were identified via verbal autopsy, which was done on all those who died within the study areas. FINDINGS: There were 636 strokes during the 3-year period (453 in Hai and 183 in Dar-es-Salaam). Overall crude yearly stroke incidence rates were 94.5 per 100,000 (95% CI 76.0-115.0) in Hai and 107.9 per 100,000 (88.1-129.8) in Dar-es-Salaam. When age-standardised to the WHO world population, yearly stroke incidence rates were 108.6 per 100 000 (95% CI 89.0-130.9) in Hai and 315.9 per 100,000 (281.6-352.3) in Dar-es-Salaam. INTERPRETATION: Age-standardised stroke incidence rates in Hai were similar to those seen in developed countries. However, age-standardised incidence rates in Dar-es-Salaam were higher than seen in most studies in developed countries; this could be because of a difference in the prevalence of risk factors and emphasises the importance of health screening at a community level. Health policy makers must continue to monitor the incidence of stroke in sub-Saharan Africa and should base future funding decisions on such data. FUNDING: The Wellcome Trust.