AIM To determine regions of reduced brain metabolism in patients with myotonic dystrophy type 1 (DM1) and type 2 (DM2) using 18F-fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET), and to analyse their potential association with cognitive deficit. METHOD Study included 29 patients (16 DM1 and 13 DM2). FDG-PET and detailed neuropsychological testing were performed in both groups. RESULTS The most common cognitive findings were executive, visuospatial, and naming dysfunction in DM1, and executive and naming dysfunction in DM2. FDG-PET showed the most prominent glucose hypometabolism in prefrontal, temporal, and pericentral regions in both DM1 and DM2 patients, with additional affection of insula and subcortical grey matter in DM2. In DM1 patients, we found association between right frontotemporal hypometabolism and executive dysfunction (p<0.05). In DM2 patients attention deficit was in association with prefrontal, insular, and striatal hypometabolism, as well as right frontotemporal hypometabolism (p<0.05). Executive dysfunction in DM2 was more common in patients with prefrontal and insular hypometabolism, right parietotemporal and frontotemporal hypometabolism, as well as left striatal hypometabolism (p<0.05). Patients with parietotemporal defect on FDG-PET were more likely to have naming dysfunction (p<0.01). CONCLUSION FDG-PET findings corresponded well with the results of neuropsychological testing. FDG-PET may be a good biomarker of central nervous system involvement in DM1 and DM2, but this hypothesis will have to be more strongly supported by larger studies.