Backround: The purpose of this article is to describe the prevalence of microvascular (retinopathy, nephropathy and neuropathy) and acute diabetic complications, and the metabolic control status, in Catalonian patients with type 1 diabetes mellitus ten years after diagnosis. Materials/Methods: We performed a cross-sectional population study evaluating 427 Type 1 diabetic patients diagnosed between 1987 and 1988 in 15 hospitals in Catalonia. 278 subjects were located, and all the study parameters were collected from their hospital medical records. Mean age at onset was 13.8 +/- 6.9 years, and 56.5% were male. The mean age of the patients was 24.8 +/- 6.7 years. Albumin excretion rate (AER), plasma creatinine, lipid profile, glycosilated hemoglobin (HbA(lc)), blood pressure, presence of retinopathy and clinical polyneuropathy, and diabetes control were evaluated. Results: The mean HbA(lc) was 7.8 +/- 1.7%. HbA(lc) was <7.5% in 48% of patients and >10% in 11.5%. The prevalence of retinopathy was 7.6%. An AER higher than 20 mug/min was found in 10.4%. Neuropathy was present in 4.3%. A significant association between microvascular complications as a whole (retinopathy and/or microalbuminuria and/or clinical polyneuropathy) and HbA(lc), (p=0.04) and hypertension (p=0.04) was observed. There were no differences in diabetic complications regarding sex or age at presentation. Conclusions: This is one of the first studies in which the prevalence of diabetic microvascular complications is reported in a South European cohort of subjects registered in EURODIAB. This population-based study confirms that complications are already present ten years after diabetes onset in a non-negligible percentage of patients.