A significant proportion of the undergraduate preparation of student nurses in the tertiary sector involves the opportunity for experience in a variety of clinical placements. The majority of nursing students in Australian universities spend time in mental health settings. This compulsory clinical experience provides the opportunity for the application of nursing theory and the development of clinical confidence. Whereas there have been attempts to quantify the attainment of confidence to perform skills in general nursing settings, there has been little attention to this issue in mental health settings. The Mental Health Nursing Clinical Confidence Scale was developed as part of a larger study aimed at investigating the impact of mental health clinical placements on undergraduate nurses' attitudes and clinical confidence. Students were surveyed using the scale before and after a mental health nursing placement. The scale revealed robust psychometric properties. Significant changes in the self-reported confidence levels of students were found at the completion of the clinical placement. A number of key factors impacted on student confidence levels both before the clinical and after the placement. The 20 item scale will be a useful instrument in future evaluations of the effectiveness of student learning in mental health settings.