OBJECTIVE - The aim of this study was to estimate the prevalence of the metabolic syndrome in Finnish type 1 diabetic patients and to assess whether it is associated with diabetic nephropathy or poor glycemic control. RESEARCH DESIGN AND METHODS - In all, 2,415 type 1 diabetic patients (51% men, mean age 37 years, duration of diabetes 22 years) participating in the nationwide, multicenter Finnish Diabetic Nephropathy (FinnDiane) study were included. Metabolic syndrome was defined according to the National Cholesterol Education Program diagnostic criteria. Patients were classified as having normal albumin excretion rate (AER) (n = 1,261), microalbuminuria (n = 326), macroalbuminuria (n = 383), or end-stage renal disease (ESRD) (n = 164). Glycemic control was classified as good (HbA1c <7.5%), intermediate (7.5-9.0%), or poor (>9.0%). Creatinine clearance was estimated with the Cockcroft-Gault formula. RESULTS - The overall prevalence of metabolic syndrome was 38% in men and 40% in women. The prevalence was 28% in those with normal AER, 44% in microalbuminuric patients, 62% in macroalbuminuric patients, and 68% in patients with ESRD (P < 0.001). Patients with metabolic syndrome had a 3.75-fold odds ratio for diabetic nephropathy (95% CI 2.89-4.85), and all of the separate components of the syndrome were independently associated with diabetic nephropathy. The prevalence of metabolic syndrome was 31% in patients with good glycemic control, 36% in patients with intermediate glycemic control, and 51% in patients with poor glycemic control (P < 0.001). Similarly, metabolic syndrome increased with worsening creatinine clearance. CONCLUSIONS - The metabolic syndrome is a frequent finding in type 1 diabetes and increases with advanced diabetic nephropathy and worse glycemic control.