Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by diffuse proximal and distal weakness due to deletion of the survival motor neuron (SMN) gene localized on chromosome 5 (5q11.2-13.3). SMA has been considered as a pure lower motor neuron disorder, and a definitive diagnosis can be established by molecular genetic testing. Here, we describe two patients with severe hypotonia and frequent aspirations at early infancy. Nerve conduction studies showed more extensive sensory involvement in these patients diagnosed to have SMA by genetic study than in classical cases of SMA. To the best of our knowledge, this is the first report of SMA Type 1 with sensory nerve involvement in Korea.