Objective. Outcome measurement in mental health services is an area of considerable clinical interest and policy priority. This study sought to assess the Behaviour and Symptom Identification Scale-24 (BASIS-24©), a brief, patient self-reported measure of psychopathology and functioning, in a UK sample, including establishing population norms for comparative purposes. Methods. Participants were 588 adults recruited from psychiatric inpatient, outpatient and primary care settings; and 630 adults randomly sampled from primary care lists who completed the BASIS-24©, and the Brief Symptom Inventory (BSI) at two time points. Results. BASIS-24© demonstrated adequate reliability (coefficient α values for combined clinical sample across subscales ranged from 0.75 to 0.91), validity and responsiveness to change (effect size for change of the BASIS-24© was 0.56 compared with 0.48 for BSI Global Severity Index). Population norms were established for the general population and adult in-patients (at in-take). The scale proved straightforward to complete across clinical settings. Variable rates of questionnaire distribution across clinical settings highlighted the ongoing challenge of incorporating outcome measures in clinical settings. Conclusion. BASIS-24© is a brief, easily administered, self-complete measure of mental well-being and functioning that adequately meets the requirements of reliability, validity and responsiveness to change required of an outcome measure.