Method
The medical records of thirty one patients, who were diagnosed as SMA by electromyography or muscle biopsy from January 1987 to December 1999, were reviewed retrospectively. Classification of SMA was mainly based on age at onset and achieved milestones.

Results
Patients with SMA type I, II and III were 17 (54.8%), 7 (22.6%) and 3 (9.7%) respectively. Four patients were unclassifiable due to functional improvements. Two patients who were classified as SMA type I, had achieved ability to sit unaided at last follow up (at 20 months and 24 months old). Two patients who were classified as SMA type II, could walk independently at last follow up (at 34 month and 26 years old). In three of SMA type I patients, functional improvements of rolling over and head control were achieved.

Conclusion
Classification of SMA based on age at onset and achieved milestones was helpful in prediction of prognosis. But 12.9% of SMA patients were not classifiable due to unexpeceted functional improvement. (J Korean Acad Rehab Med 2003; 27: 38-42)