We estimated the prevalence of type 2 diabetes in the Islamic Republic of Iran by systematic review of all available studies in the country between 1996 and 2004 and aggregation of the data using meta-analysis and meta-regression methods. In those > 40 years the prevalence was 24% and it increased by 0.4% with each year after 20 years of age. The risk of type 2 diabetes was 1.7% greater in women than men (P < 0.001). The prevalence of type 2 diabetes appears higher in the Islamic Republic of Iran than in other developing countries but because of differences in age pyramids, the crude prevalence is not an appropriate indicator and age-adjusted or age-specific prevalences should be used.