Background: Pain-related fear is related to disability in persistent pain conditions. Exposure treatment has been reported to be of great benefit in replicated single case experiments. Aim: To evaluate the effects of exposure in vivo on fear and function in patients with persistent pain and work disability. Method: We recruited 46 patients suffering from long-term back pain and reduced function, who also were deemed fearful according to standardized measures. Participants were randomized into either an exposure plus usual treatment or waiting list control plus usual treatment group. After the waiting period the control group crossed over and received the exposure treatment. Results: Between group comparisons showed a significantly better result for the exposure group on function, but not for fear or pain and effect sizes were modest (function = .6; fear = .4; pain =. 1). When the control group crossed over to treatment significant treatment effects were noted for fear and function. For all patients treated, the pre to post-treatment effect sizes were large (function = .7; fear = 1.1; pain = .9). There were 12 dropouts (8 in exposure and 4 in the control) during the first treatment phase and an additional 4 when the control group crossed over to exposure. Conclusions: Compared to a group receiving usual treatment and waiting for exposure, the exposure in vivo group demonstrated a significantly larger improvement on function. Overall exposure had moderate effects on function, fear and pain intensity. We conclude that exposure may be important in treatment, but is not recommended as a "stand alone" adjunct to usual treatment.