The role of physical activity for patients with amyotrophic lateral sclerosis (ALS) is controversial. Twenty-five ALS patients were randomized to receive a moderate daily exercise program (n=14) or not to perform any physical activity beyond their usual daily requirements (n=11). At baseline and after 3, 6, 9 and 12 months, patients were assessed by manual muscle strength testing, the Ashworth spasticity scale, ALS functional rating scale (FRS), fatigue severity scale, a visual analogue scale for musculoskeletal pain and the quality-of-life scale (SF-36). At 3 months, patients who performed regular exercise showed less deterioration on FRS and Ashworth scales, but not on other parameters. At 6 months, there was no significant difference between groups, although a trend towards less deterioration in the treated group on most scales was observed. At 9 and 12 months, there were too few patients in each group for statistical evaluation. Our results show that a regular moderate physical exercise program has a short-lived positive effect on disability in ALS patients and should be recommended.