Double diabetes is the association between type 1 diabetes mellitus (DM1) and metabolic syndrome (MS). The prevalence of hypertension, dyslipidemia, central obesity and macrovascular complications has increased in DM1 patients, regardless glycemic control. To determine the prevalence of MS in patients with DM1. We performed a descriptive cross-sectional study of clinical characteristics of DM1 patients. Biochemical and anthropometric parameters were determined and the presence of hypertension, dyslipidemia and central obesity were assessed. MS was defined according to American Heart Association/National Heart, Lung and Blood Institute (AHA/NHLBI) and National Cholesterol Education Program: Adult Treatment Panel III (NCEP:ATPIII) criteria. For this study 130 patients were evaluated (66% women) with a median age of 29.5 years (interquartile range [RI]: 22-36) and disease evolution of 12 years (RI: 7-17). 47% had dyslipidemia, 23% hypoalphalipoproteinemia, 11% hypertrigliceridemia and 13% both pathologies. Additionally 64% had high level of low-density lipoprotein cholesterol (C-LDL) and 21% had hypertension. According to AHA/NHLBI criteria, 37.5% (with three parameters) and 14% (more than three parameters) of patients were estimated to have MS. On the other hand, using NCEP:ATPIII criteria 25% (three parameters) and 11.5% (more than three parameters) had MS. Patients with DM1 and MS were older, heavier and had greater body mass index (BMI) and waist circumference. The presence of MS in patients with DM1 is evident in our study. There are no differences in glycosylated hemoglobin or insulin doses between groups with and without MS.