In spite of the development of modern imaging, most lesions of tuberous sclerosis (TS) remain difficult to detect before birth. Particularly, brain involvement at a fetal stage of development is poorly documented. We report three cases of fetuses examined after pregnancy was interrupted because of the detection of cardiac rhabdomyoma. In two of the three cases there were brain lesions suggestive of TS, including cortical tubers, subependymal nodules and scattered bizarre giant cells in the white matter. These observations confirm that brain lesions of TS can be present before birth; they can show, at an early period of development, an aspect quite similar to lesions described at an adult stage. The most characteristic cell abnormality is the so-called balloon cell. The majority of these cells exhibit a strong immunoreactivity with glial antibodies (GFAP, vimentin, S100). Immunoreactivity with neuronal markers (synaptophysin) is present in a small percentage of balloon cells.