Objective: To conduct a formal economic evaluation of various dosages of psychotherapy for patients with avoidant, dependent, and obsessive-compulsive (ie, cluster C) personality disorders (Structured Interview for DSM-IV Personality criteria). Method: We developed a decision-analytic model to assess the cost-effectiveness of 5 dosages of psychotherapy (ie, long-term outpatient psychotherapy, short-term and long-term day hospital psychotherapy, and short-term and long-term inpatient psychotherapy) over a 5-year time horizon in terms of cost per recovered patient-year and cost per quality-adjusted life-year (QALY). Model parameters were estimated using data from 466 patients with cluster C personality disorders who were admitted to 6 specialist centers of psychotherapy in The Netherlands and assigned to 1 of the 5 treatment groups. Probabilistic analysis was conducted to explore the stability of results over uncertain data ranges. Analyses were conducted from both societal and payer perspectives. Results: From the societal perspective and below a threshold of (sic) 2,637 (US $3,351.92) per recovered patient-year, short-term day hospital psychotherapy resulted in the highest level of benefit for its cost; above the threshold, short-term inpatient psychotherapy was the most cost-effective choice. In terms of cost per QALY, this switch point was at a threshold value of (sic)16,570 (US $21,062.29) per QALY. From the payer perspective, the optimal strategy changed from short-term day hospital psychotherapy to short-term inpatient psychotherapy at threshold values of (sic) 9,874 (US $12,550.94) per recovered patient-year and (sic) 66,302 (US $84,277.13) per QALY. Conclusions: This study indicates that short-term day hospital psychotherapy and short-term inpatient psychotherapy are the most cost-effective treatment strategies for patients with cluster C personality disorders. The ultimate selection depends on what cost-effectiveness threshold is considered acceptable and what perspective is adopted. Trial Registration: controlled-trials.com Identifier: ISRCTN73817429 J Clin Psychiatry 2011;72(1):51-59 (C) Copyright 2010 Physicians Postgraduate Press, Inc.