Shock wave therapy has been used for treatment of several soft tissue disorders that are characterized by chronic pain. We sought to determine if shock wave therapy reduces chronic Achilles tendon pain. Forty-nine patients were enrolled in a double-blind randomized placebo-controlled trial. Each patient was treated once a month for 3 months. The primary outcome measure was a reduction in Achilles tendon pain during walking. At the end of the trial, we found no difference in pain relief between the shock wave therapy group and the control group. There were two patients (62 years and 65 years) with tendon ruptures in the treatment group, suggesting caution when treating older patients. These results provide no support for the use of shock wave therapy for treatment of patients with chronic Achilles tendon pain. However, the confidence intervals include the potential for a clinically relevant treatment effect. LEVEL OF EVIDENCE: Therapeutic study, Level I (systematic review of Level I RCTs-and study results were homogenous). See the Guidelines for Authors for a complete description of levels of evidence.