Two children of second-cousin parents were found to have a very mild form of Morquio syndrome. The 14-year-old boy was 147 cm tall and had fine corneal deposits, a broad chest, dislocated hips, and flat feet. His 7-year-old sister had a broad chest but otherwise normal physical development. An abnormal lumbar spine was seen in radiographs of both children. Analysis of the urine from the affected children showed levels of acid mucopolysaccharides (AMPS) up to twice as high as that found in normal urine, but no evidence of keratosulfaturia. Most urinary AMPS was chondroitin-6-sulfate. Multiple assays of N-acetylgalactosamine-6-sulfate (GalNAc-6-SO4) sulfatase in leukocytes and cultured skin fibroblasts showed deficiency of this enzyme in the range found in the classical form of Morquio (Morquio A) syndrome. This report identifies an enzymatic defect in one form of non-keratan-sulfate-excreting Morquio (NKSE Morquio) syndrome and confirms the absence of keratosulfaturia in this mild form of Morquio disease.