Two nonconsanguineous patients affected by I-cell disease (mucolipidosis II) are reported. I-cell disease, an oligosaccharidosis, is characterized by severe psychomotor retardation, marked shortness of stature, coarse facies, gingival enlargement, generalized bone demineralization, periosteal cloaking of long bones visible in early infancy, a rapid deteriorating course, and death from heart failure or bronchopneumonia, usually by the age of 5 years. This disorder is the result of a deficiency of glycoprotein N-acetylglucosaminylphosphotransferase activity, necessary for proper intracellular processing of lysosomal enzymes. Inheritance is autosomal recessive. It received the name I-cell disease because of several granular inclusions in the cytoplasm of cultured fibroblasts and amniotic fluid cells observed under phase contrast microscopy. These granules represent altered lysosomes. The two patients, reported here, had a very marked gingival hypertrophy and, for this reason, were referred to the Oral Pathology Service of Galliera Hospital. A gingivectomy was performed on patient 2 to improve the mastication, but few months later gingival hypertrophy reappeared.