Tuberous sclerosis (TS) is an autosomal dominant disorder with a high rate of de novo mutation. The real difficulty is to ascertain the diagnosis and to give the neurological prognosis in each case. Prenatal diagnosis of TS is generally based on ultrasonographic signs of multiple cardiac tumours, i.e. rhabdomyomas. Recent progress in magnetic resonance imaging (MRI) enables the diagnosis in a large proportion of cases based on typical brain lesions. It may have a role in the prenatal management of TS, although MRI images seem to underestimate the anatomical findings. Two cases in which TS was diagnosed prenatally are presented with reference to the value of MRI in the prenatal management and comparison with anatomical findings.