There are currently no published scales to assess the attitudes of students and professionals across a wide range of healthcare disciplines towards people with mental illness. Secondary analysis from a randomised controlled trial (RCT) of anti-stigma interventions was carried out to test the reliability, validity and acceptability of the Mental Illness: Clinicians' Attitudes (MICA) v4 scale, a modification of the MICA v2 scale in a sample of 191 nursing students. The MICA v4 was found to have good internal consistency (α=0.72) and item-total correlations. Principal component analysis produced a five-factor structure and the scale had acceptable convergent validity. A group of students and professionals within the healthcare discipline (n=5) reported that the MICA v4 had good face validity and suggested its use with students and professionals working in non-mental health settings. The scale had low rates of missing data, good readability and took less than 4min to complete. The MICA v4 scale was found to be a reliable, valid and acceptable measure of foundation year nursing students' attitudes towards mental illness. It has the potential for use with students and qualified staff across a range of healthcare professions and is available for use from the authors.