Forty-five African children with SMA were seen over a period of five years. Fifteen had severe infantile form (Group 1), 19 intermediate (Group 2), 9 juvenile (Group 3) and 2 cervical type. A positive family history was obtained in only 9% of patients. The female/male ratio was 1:1.7. The age of onset was under four months in Group 1, between 5-24 months in Group 2. In 77% of Group 3 onset was between 5-24 months, 22% between 25-48 months. The lower limbs were more severely affected than upper limbs in all except the two patients with cervical SMA, proximal muscles more than distal in 82% and proximal and distal muscle were equally affected in 18%. Bulbar weakness was present in 73% and facial weakness in 80% of Group 1 patients only. Fasciculation of tongue occurred in 50% of Group 1, 42% of Group 2 and 44% of Group 3 patients. Tremor of hands was seen in none of the patients in Group 1, 58% in Group 2 and 66% in Group 3. Tendon reflexes were absent or depressed in all except one patient in Group 2 and were normal in the legs of the two patients with cervical SMA. The blood CK was elevated in 26% of patients. An ECG "tremor" was present in 26% of patients in Group 1, 68% in Group 2 and 66% in Group 3. Four patients (all in Group 1) died of pneumonia; the outcome in the others is not known.(ABSTRACT TRUNCATED AT 250 WORDS)