The aim of this study is to evaluate 75 patients affected by childhood-onset spinal muscular atrophy (SMA), using the diagnostic criteria and classification recently suggested by the International SMA Collaboration Consortium. Sex predominance, age of onset, clinical evaluation and other relevant clinical data of the disease are reported. These findings, as well as the role of the EMG and muscle biopsy as diagnostic tools, are discussed. The study suggests that the frequency of SMA in some areas of Sicily is high, possibly correlating with a relatively high gene frequency.