This study of clinical outcome in amyotrophic lateral sclerosis (ALS) evaluated 148 patients (93 men and 55 women) diagnosed in Hordaland county, Norway, during the period 1970 to 1990. In addition to evaluation of clinical data, data were available on sex, age at diagnosis, time from appearance of symptoms to diagnosis, family history, EMG and spinal fluid. Sixty-nine cases were bulbar ALS and 79 were spinal ALS. Median survival from diagnosis was 16.5 months, 26.0 months in the spinal and 12.1 months in the bulbar form. The survival time decreased with increasing age at the start of disease. A brief interval from start of symptoms to diagnosis was also a poor prognostic factor. Cases with mainly spastic clinical appearance had longer survival than those with marked atrophy. Sex, appearance of familial cases, increased protein level in the spinal fluid, or disease confirmed or not by EMG had no influence on the prognosis. The importance of the prognostic variables was assessed simultaneously using a proportional hazards model. To test the validity of the prognostic factors, a binary survival outcome was established and a predictive rule determined by logistic regression. The data were applied on 11 ALS cases collected outside Hordaland county. Only 1 out of 7 patients with a predicted probability of living more than 1 year actually died within this time period. Two out of 4 patients in the poor prognostic group were dead within a year from the time of diagnosis.