This study estimates the prevalence of known diabetes, and complications of type 2 diabetes, among subjects aged 35-64 years, in relation to socio-economic factors and gender at four primary health care centres (PHCCs) in Stockholm County, Sweden. A total of 685 diabetic subjects aged 35-64 years of age were identified in primary care by diagnosis using electronic patient records. Data were supplied from medical records, and postal questionnaires. The prevalence of known diabetes among subjects aged 35-65 years differed between the PHCCs, with standardised rates between 1.7 and 3.6%, with the highest figure at the PHCC in an underprivileged area. The prevalence was higher among men (2.8% versus 1.7%). A subgroup of the patients, i.e. 389 subjects aged 35-64 years with type 2 diabetes, was studied with regard to complications. Higher education level was protective for microvascular complications (OR 0.50; CI 0.25-1.00). In addition, microvascular complications were predicted by male sex, duration, HbA(1c), and hypertension, and macrovascular complications by male sex, age, and hypertension. Prevalence of known diabetes and microvascular complications in type 2 diabetes, are associated with lower socio-economic status and male sex.