Generalized gangliosidosis, or GM1 gangliosidosis, is associated with the lysosomal storage of the monosialoganglioside GM1. This disorder results from a deficiency of the enzyme β-galactosidase. In the infantile form, dysmorphic facial features, hypotonia, feeding difficulties, hepatosplenomegaly, bone deformities, and macular cherry red spots may be present. Ultimately patients with infantile GM1 gangliosidosis develop spasticity. Seizures can occur in the later stage of disease. Mongolian spots are birth marks with irregular shapes. The sacral area is the classic site of involvement and spots usually disappear in a few years. Extensive Mongolian spots involve large areas over the entire posterior and anterior aspects of the extremities and trunk. This condition is associated with inborn errors of metabolism such as mucopolysaccharidosis and GM1 gangliosidosis. We present an infant with extensive Mongolian spots in association with GM1 gangliosidosis. Anahtar Kelimeler : GM1 gangliosidosis, yaygın mongol lekeleri, hipotonik infant, GM1 gangliosidosis, extensive Mongolian spots, hypotonic infant