We present the clinical and neuroimaging findings of five patients (four males, one female; mean age 12 years) affected by congenital myotonic dystrophy and the correlation with their molecular genetic analysis. At birth all five presented severe muscular weakness and hypotonia, associated with feeding difficulties and respiratory distress. In the same patients, congenital clubfoot or more generalized arthrogryposis was also evident. Lymphocyte DNA was characterized in each by a CTG repeat longer than 1300 in the region of the myotonic dystrophy gene in chromosome 19. The patients' neurological condition was evaluated by clinical examination, intelligence tests, electroencephalography, and brain magnetic resonance imaging. All five suffered from some impairment of intellectual function (IQ ranged from 52 to 79). In three a longitudinal evaluation of the cognitive deficit detected no deterioration. In all patients magnetic resonance imaging showed some degree of ventricular dilatation, loosely correlated to the cognitive impairment; in three there was hypoplasia of the corpus callosum and in two mild abnormalities of supratentorial white matter. The relationship between the size of the CTG repeat expansion found in lymphocyte DNA and the cerebral abnormalities appeared inconsistent in this unusual myoencephalopathy of the newborn.