Clinical supervision is widely accepted as an essential prerequisite for high quality nursing care. This paper reports findings from a study that aims to identify the factors that may influence the effectiveness of clinical supervision for community mental health nurses (CMHNs) in Wales, UK. Two hundred and sixty (32%) CMHNs from an estimated total population of 817 completed the Manchester Clinical Supervision Scale (MCCS) and a demographic questionnaire. The MCCS is a 36-item questionnaire measuring the quality and effectiveness of the supervision received. Three-quarters of CMHNs reported having participated in six or more sessions of supervision in their current posts. Clinical supervision was more positively evaluated where sessions lasted for over one hour, and took place on at least a once-monthly basis. Perceived quality of supervision was also higher for those nurses who had chosen their supervisors, and where sessions took place away from the workplace. These findings have important implications for the organization and delivery of mental health nursing services.