OBJECTIVE To determine the frequency of metabolic syndrome (MS) and insulin resistance (IR) in first-degree relatives of type 1 diabetic patients (FDR1) and to study the relationship between these two disorders and some clinical, biochemical and immunological characteristics. METHODS We studied 289 persons, of which 193 were children/adolescents and 96 were adults. Weight, height, waist and hip circumference, blood pressure, blood glucose, insulin, cholesterol, triglycerides, high-density lipoprotein-cholesterol, glutamic acid decarboxylase autoantibodies (GADA) and tyrosine phosphatase autoantibodies were determined. IR was assessed through the insulin resistance index (HOMA-IR). The criteria of the World Health Organization for adults and the Cuban consensus for children and adolescents were used to define MS. RESULTS The prevalence of MS in child and adolescent FDR1 was 5.7% (11/193) while IR was found in 24.9% (48/193). For adult FDR1, the frequency of MS was 6.2% (6/96) and that of IR was 14.6% (14/96). Interestingly, an association was found between IR and MS in adults but not in children and adolescents. IR was more frequent in children and adolescents than in adults (p<0.05). The presence of GADA was associated with IR but not with MS (p<0.05). CONCLUSIONS The frequency of MS in child and adolescent FDR1 was similar to that found in the general population according to studies using similar definitions of MS. In contrast, the frequency of MS in adults was lower than that reported in Cuba for the first-degree relatives of patients with type 2 diabetes. IR was not only associated with MS in first-degree relatives. The association of IR with the presence of GADA may reflect the fact that beta cell hyperactivity increases autoantigen expression.