OBJECTIVE:To study the clinico pathologic features of childhood spinal muscular atrophy (SMA) and its significance. METHODS: The clinical and pathogic data of 42 patients with SMA Ⅰ Ⅲ were studied retrospectively. Routine histological and histochemical methods were used in muscular biopsy. RESULTS: The severity of the illness was positively related to the age of onset: the earlier the onset, the more serious the illness. There were different pathologic changes among the different types of SMA. SMA Ⅰ displayed large group round atrophic fibers and showed an incomplete type grouping; usually both type 1 and type 2 fibers were involved. The large group atrophic fibers were rarely found and the type grouping was obvious in SMA Ⅱ. The pathologic changes of SMA Ⅲ varied, and the type grouping was a major feature. CONCLUSIONS: The diagnosis of SMA could be made by combining the clinical manifestation with electroencephalography and muscular biopsy.