N-Acetylgalactosamine-6-sulfate sulfatase (GALNS) catalyzes the first step of intralysosomal keratan sulfate (KS) catabolism. In Morquio type A syndrome GALNS deficiency causes the accumulation of KS in tissues and results in generalized skeletal dysplasia in affected patients. We show that in normal cells GALNS is in a 1.27-MDa complex with three other lysosomal hydrolases: -galactosidase, ␣-neuraminidase, and cathepsin A (protective protein). GALNS copurifies with the complex by different chromatography techniques: affinity chromatography on both cathepsin A-binding and -galactosidase-binding columns, gel filtration, and chromatofocusing. Anti-human cathepsin A rabbit antiserum coprecipitates GALNS together with cathepsin A, -galactosidase, and ␣-neuraminidase in both a purified preparation of the 1.27-MDa complex and crude glycoprotein fraction from human placenta extract. Gel filtration analysis of fibroblast extracts of patients deficient in either -galactosidase (-galactosidosis) or cathepsin A (galactosialidosis), which accumulate KS, demonstrates that the 1.27-MDa complex is disrupted and that GALNS is present only in free homodimeric form. The GALNS activity and cross-reacting material are reduced in the fibroblasts of patients affected with galactosialidosis, indicating that the complex with cathepsin A may protect GALNS in the lysosome. We suggest that the 1.27-MDa complex of lysosomal hydrolases is essential for KS catabolism and that the disruption of this complex may be responsible for the KS accumulation in -galactosidosis and galactosialidosis patients.