Many Medicaid programs have either fully or partially carved out mental health services. The evaluation of carve-out plans requires a case-mix model that accounts for differing health status across Medicaid managed care plans. This article develops a diagnosis-based case-mix adjustment system specific to Medicaid behavioral health care. Several different model specifications are compared that use untransformed, square root transformed, and log-transformed expenditures. (Contains 5 tables and 10 notes.)