Tuberous sclerosis is an autosomal dominant disease with variable expression. The initial manifestations have been reported at varying stages postnatally, but little is known about the fetal age at which the disease may be detected. The antenatal ultrasonographic features in 2 affected fetuses, at 40 and 26 weeks respectively, are reported. The second case appears unique because of the early fetal involvement and the abnormally large brain tumour.