We report the rationale, reliability, validity and responsiveness studies of the Mental Illness: Clinicians' Attitudes (MICA) Scale, a 16-item scale designed to measure attitudes of health care professionals towards people with mental illness.Items were generated through focus groups with service users, carers, medical students and trainee psychiatrists. Psychometric testing was completed in a number of student samples. The responsiveness of the scale was tested after a 1.5 h mental illness stigma related intervention with medical students.The MICA scale showed good internal consistency, alpha = 0.79. The test-retest reliability (concordance) was 0.80 (95% CI: 0.68-0.91). The standardised response mean for the scale was 0.4 (95% CI 0.02-0.8) after a mental illness related stigma intervention.The MICA scale is a responsive, reliable and valid tool, which can be used in medical education and mental health promotion settings and studies.