Spinal muscular atrophy(SMA) is an autosomal recessive disease characterized by diffuse proximal and distal weakness due to the deletions of the survival motor neuron(SMN) genes localized on the chromosome 5(q11.2-q13.3). One hypothesis is that the cause of SMA is a pathologic continuation of a process of programmed cell death that is normal in are embryonic life. The SMN genes are supposed to arrest apoptosis(programmed cell death) of motor neuroblasts. SMA is traditionally considered as a pure lower motor neuron disorder, for which a current definitive diagnosis can be established by a molecular genetic testing. We report a case of a female infant with severe hypotonia and frequent aspiration at the age of four months. She was diagnosed as SMA by a genetic study, but the nerve conduction studies showed more extensive sensory involvement in this case other than other classical cases of spinal muscular atrophy. To our knowledge, this is the first report of SMA with sensory nerve involvement in Korea.