Carpal tunnel syndrome (CTS) and fibromyalgia (FM) are common diseases in adult women. The aim of this study was to investigate the effect of FM on the outcome of local steroid treatment in patients with CTS. Forty-eight female patients with CTS and 26 female patients with CTS who also met the 1990 American College of Rheumatology (ACR) criteria for FM were enrolled the study. All patients underwent single steroid injections into the carpal tunnel. Response to injection was measured using Boston Questionnaire (BQ) and electrophysiological tests. The BQ scores and electrophysiological findings showed significant improvement 3 months after the treatment in both groups (P<0.001). However, less improvement in BQ symptom severity scores was observed in the FM group than the other group (P<0.05). Bilateral CTS was also more common in the FM group (P<0.05). The present data suggest that FM must be kept in mind in patients with CTS giving poor response to local steroid treatment.