A prospective, case-control study was carried out on 25 patients with myotonic dystrophy (MyD) and 25 healthy subjects using brain magnetic resonance imaging (MRI). The frequency and severity of white matter hyperintense lesions (WMHL) and brain atrophy in MyD patients were compared with their clinical features and cognitive impairment using an extensive neuropsychological battery. Eighty-four per cent of MyD patients showed WMHL, compared with 16% of controls (p < 0.0001). These lesions involved all cerebral lobes, without hemispheric prevalence. Twenty-eight per cent of MyD patients also showed particular WMHL at their temporal poles. Myotonic patients had significantly more cortical atrophy than controls. No relationship between atrophy and WMHL was found on the MRI scans. The extent of brain abnormalities (WMHL or atrophy) was not correlated to age, disease duration, physical disability or severity of neuropsychological impairment. Central nervous system abnormalities revealed by MRI appear to be an almost constant feature of MyD, but they are not found to be related to clinical or cognitive parameters. Their nature is still unclear: some of them, located at the temporal poles, seem to be characteristic of the disease, while others small, diffuse WMHLs, similar to the age related alterations revealed by MRI occurring during young and adult age in MyD patients.