I report 2 unusual cases of Proteus syndrome that support the concept of somatic mosaicism. In one patient, a huge connective tissue nevus covered the chest and abdomen and hyperostoses of the calvaria were observed. In the other patient, linear verrucous epidermal nevi, epibulbar dermoids, and hyperostoses were found. No enlargement of the limbs or digits occurred and the plantar surfaces of the feet were normal. Selective aspects of Proteus syndrome not previously reviewed are also presented including: uncommon neoplasms; pulmonary and renal abnormalities; brain malformations; facial phenotype associated with seizures and severe mental deficiency; and types of abnormal growth in the craniofacial skeleton.