Three siblings with Morquo's syndrome are described. Cultured fibroblasts from the youngest sibling demonstrated a total absence of N-acethylgalactosamine-6-sulphate-sulphatase whereas beta-galactocidase activity was normal, thus verifying the diagnosis of MPS-IV A. Dental features such as pointed cusps, spade-shaped incisors, thin enamel and pitted buccal surfaces were observed in all three children. Furthermore, in all three siblings the TMJ was affected with severe resorption of the head of the condyle. Histological examination of exfoliated primary molars showed a band of increased porosity following the striae of Retzius in the outer part of the enamel. These developmental disturbances were occasionally associated with minor localized defects in the enamel surface. The importance of close monitoring of dental development and regular dental care in order to prevent attrition of the teeth, loss of vertical face height and subsequent risk of TMJ dysfunction is emphasized.