Clinical features and associations of 560 cases of motor neuron disease. In 560 cases of motor neuron disease, studied retrospectively from their case notes in three teaching centres, the age at onset ranged from 13 to 87 years (mean 56 years), and the mean duration of illness until death was 2.6 years. In the subgroup of the disease presenting with progressive bulbar palsy presenting after age 59 years, there was a previously unrecognised excess of females sufficient to equalize the sex ratio of incidence of the disease in this age group. No potentially causative clinical associations emerged; no relation was noted between occupational exposure to leather products, trauma or surgical procedures and the disease. There was a trend for patients with motor neuron disease to give a history of abstention from alcohol. 