Spinal Muscular Artophy is the most common cause of floppy infant syndrome, and is characterized by flaccid paralysis with muscle atrophy that is due to progressive degenerative change of anterior horn cell of spine.

We experienced 3 cases of spinal muscular atrophy, type II confirmed by electrodiagnostic study and muscle biopsy and then, brief summaries of clinical manifestation, laboratory data, electrodiagnostic study and muscle biopsy frundings were reviewed.