Background. The understanding of obesity as a growing health problem in Africa and Tanzania in particular is hampered by lack of data as well as sociocultural beliefs in which overweight and obesity are revered. This study sought to determine the prevalence of overweight and obesity among primary school children aged 8–13 years in Dar es Salaam, Tanzania. Method. A cross-sectional analytical research design was used to study overweight and obesity in primary schools in Dar es Salaam, Tanzania. The target population was 150,000 children aged 8–13 years. Stratified random sampling was used to select 1781 children. Weight and height were taken and WHO standards for children were used to determine weight status. Results. Findings showed that the prevalence of overweight and obesity was 15.9% and 6.7%, respectively (N = 1781). However, 6.2% of the children were underweight. There were significant differences in mean BMI between children in private and public schools (p = 0.021), between male and female (p < 0.001), and across age groups of 8–10 and 11–13 years (p < 0.001). Conclusion. The prevalence of overweight and obesity among primary school children is significant and requires management and prevention strategies.