Objectives We aimed to estimate the prevalences of diabetes and impaired fasting glucose (IFG) in a national sample in Peru and assess the relationships with selected sociodemographic variables. Methods We estimated prevalence in PERUDIAB study participants, a nationwide, stratified urban and suburban population selected by random cluster sampling. Between 2010 and 2012, questionnaires were completed and blood tests obtained from 1677 adults =25 years of age. Known diabetes was defined as participants having been told so by a doctor or nurse and/or receiving insulin or oral antidiabetic agents. Newly diagnosed diabetes was defined as fasting plasma glucose =126 mg/dL determined during the study and without a previous diabetes diagnosis. IFG was defined as fasting plasma glucose of 100–125 mg/dL. Results The estimated national prevalence of diabetes was 7.0% (95% CI 5.3% to 8.7%) and it was 8.4% (95% CI 5.6% to 11.3%) in metropolitan Lima. No gender differences were detected. Known and newly diagnosed diabetes prevalences were estimated as 4.2% and 2.8%, respectively. A logistic regression response surface model showed a complex trend for an increased prevalence of diabetes in middle-aged individuals and in those with no formal education. Diabetes prevalence was higher in coastal (8.2%) than in highlands (4.5%; p=0.03), and jungle (3.5%; p<0.02) regions. The estimated national prevalence of IFG was 22.4%, higher in males than in females (28.3% vs 19.1%; p<0.001), and higher in coastal (26.4%) than in highlands (17.4%; p=0.03), but not jungle regions (14.9%; p=0.07). Conclusions This study confirms diabetes as an important public health problem, especially for middle-aged individuals and those with no formal education. 40% of the affected individuals were undiagnosed. The elevated prevalence of IFG shows that nearly a quarter of the adult population of Peru has an increased risk of diabetes.