60 cases of chronic spinal muscular atrophy (CSMA) were followed-up for a period varying from 5 to 40 years. The neuromuscular impairment was evaluated by Norris' ALS score, both at the time of last examination and retrospectively at the time of diagnosis. Age at onset of symptoms was the most important factor in the progression of the neuromuscular damage. Monomelic or asymmetric location of symptoms at the time of diagnosis and duration of the disease were not significantly correlated to the worsening of ALS score.