The objective of this study was to determine the effectiveness of a behaviour-oriented graded activity programme compared with usual care for low back pain. A total of 134 workers who were absent from work because of low back pain were randomly assigned to either graded activity or usual care. Patients in the experimental group received graded activity, a physical exercise programme based on operant-conditioning behavioural principles, to stimulate a rapid return to work. Outcomes were the number of days of absence from work because of low back pain, functional status and severity of pain. The median number of days of absence from work over 6 months of follow-up was 58 days in the graded activity group and 87 days in the usual care group. From randomisation onward, graded activity was effective after 50 days of absence from work. The graded activity group was more effective in improving functional status and pain than the usual care group. The effects, however, were small and not statistically significant.