A total of 23 patients with motor neuron disease (MND), encompassing 17 cases of amyotrophic lateral sclerosis, 4 of progressive muscular atrophy and 2 of progressive bulbar palsy, was diagnosed in Benghazi, north-eastern Libya, between 1980 and 1985. The male to female ratio was 2.3:1. The average incidence of MND was 0.89/100,000 population/year (0.87 when age and sex-adjusted to the Libyan population). Eighteen patients were alive on the prevalence day, September 15, 1985, which provided a prevalence rate of 3.47/100,000 population (3.42 if adjusted). Age-specific incidence rates were highest in the 50- to 59-year-old age group, 8.14/100,000/year for men and 6.10/100,000/year for women. The median age at the time of diagnosis was 51 years, and the median duration for the 5 dead MND patients after the onset of the disease was 30 months. The median survival time for all MND cases combined was 42 months.