BACKGROUND: There is no consensus regarding the effectiveness of Transcutaneous Electrical Nerve Stimulation (TENS) for chronic musculoskeletal or low back pain. A review of previous trial methodology identified problems with treatment fidelity. Qualitative research with experienced TENS users identified specific contexts for TENS use, leading to individualised outcomes. There is little information available to guide the selection of Patient Reported Outcome Measures (PROMs) appropriate for TENS evaluation. OBJECTIVE: To determine the capability of previously used PROMs to capture the perceived benefits of TENS reported by secondary care Pain Clinic patients who successfully used TENS to manage chronic musculoskeletal pain. DESIGN: The World Health Organisation International Classification of Functioning, Disability and Health (ICF) was used to match the perceived benefits of TENS against previously used PROMS. METHODS: Semi-structured interviews conducted with nine patients (6 women) as well as three other qualitative datasets (88 patients in total) generated patient-reported benefits which were matched against previously used PROMs using the ICF. FINDINGS: There were 18 items in the final list of benefits, and none of the four functional outcome measures used in previous RCTs captured more than 8 of these 18 items. The data analysis complemented the inductive thematic analysis but could not replace it, indicating the value of both forms of analysis. CONCLUSIONS: This study highlights a low level of match between outcome measures used in previous TENS studies, and the benefits perceived by experienced TENS users. This suggests that further work is required if the patient-reported benefits of TENS are to be evaluated.