An acceptable, standardised outcome measure to assess efficacy and effectiveness is needed across multiple disciplines offering psychological therapies. To present psychometric data on reliability, validity and sensitivity to change for the CORE-OM (Clinical Outcomes in Routine Evaluation--Outcome Measure). A 34-item self-report instrument was-developed, with domains of subjective well-being, symptoms, function and risk. Analysis includes internal reliability, test-retest reliability, socio-demographic differences, exploratory principal-component analysis, correlations with other instruments, differences between clinical and non-clinical samples and assessment of change within a clinical group. Internal and test-retest reliability were good (0.75-0.95), as was convergent validity with seven other instruments, with large differences between clinical and non-clinical samples and good sensitivity to change. The CORE-OM is a reliable and valid instrument with good sensitivity to change. It is acceptable in a wide range of practice settings.