Broad categories of adjustment to cancer were originally identified clinically. Subsequently, a self-rating questionnaire--the MAC (Mental Adjustment to Cancer) scale--was developed to measure these categories of adjustment. We report here a validation study of the MAC scale. Fifty-four consecutively referred patients with various cancers were given the MAC scale. The patients' adjustment to cancer was also rated clinically by two psychiatrists who had no knowledge of the MAC scale scores. Statistical comparisons between these scores and the clinical ratings are reported. The level of agreement obtained was 79%--Kappa 0.72.