The Mental Health Self-Direction Scale (MHSD) measures the extent to which clients are able to resolve mental problems by themselves. Because this scale had not yet been evaluated, the aims of this paper were (a) to evaluate and improve the MHSD and (b) to explore the sensitivity to change of the improved scale. The MHSD was evaluated and improved by means of confirmatory factor analyses of data from one longitudinal and two cross-sectional outpatient sample. Inconsistent items were removed in a stepwise fashion. Subsequently, the scale's sensitivity to change was explored in the longitudinal sample by using latent growth curve models. The original 31-item scale was reduced to a more stable version with 19 items that yielded four factors named: actorship, demoralization, commitment, and understanding. Throughout clients' treatment, actorship and understanding tended to increase; demoralization tended to decrease; and commitment remained consistently high. The abridged MHSD scale is stable and sensitive to change. It measures the extent to which clients experience and develop self-direction throughout their treatment. With the use of the new MHSD scale, new views on mental health that emphasize clients' ability to actively engage and cope with health-challenges can be incorporated into clinical treatment.