This randomized clinical trial was designed to determine the effect of treating low back pain as a benign, self limiting condition by light normal activity. Patients on sickness leave from work for more than 8 weeks were randomized into two groups: intervention (n = 463) and control (n = 512). Those in the intervention group were examined, provided information, and given instruction. Outcome was measured by return or failure to return to work (still on sickness leave). Survival analysis showed a highly significant (P = 0.000) reduction in sickness leave in the intervention group as compared with the control group. At 200 days 60% were still on sickness leave in the control group vs. 30% in the intervention group. A multivariate analysis with age, sex, and treatment as cofactors showed that sex had no effect on length of sickness leave and that treatment retained its effect when adjusting for differences in age composition. This study indicates that low back pain treated as a benign, self limiting condition recommended to light mobilization gives superior results as compared to treatment within a conventional medical system.