This investigation examined the cognitive factors that influence case conceptualization (CC) and treatment planning (TP) tasks among experienced mental health professionals. A thinking aloud process-tracing strategy was used to identify problem-solving styles and clinical judgment strategies used by 25 licensed psychologists, clinical mental health counselors, and clinical social workers while responding to a standardized case conceptualization and treatment planning task. Cluster analysis revealed a four cluster solution that differentiated among treatment planning scores of these clinicians. SPSS discriminant analyses identified (a) three problem-solving styles (i.e., differentiation, integration, affiliation) that correctly predicted cluster membership in 96% of cases, and (b) three clinical judgment strategies (i.e., minimal, complex, heuristic) that correctly predicted cluster membership for all of these clinicians. Implications of these findings for training and research are presented.