Assigning clients to treatments on the basis of their differential aptitudes for those treatments may reduce variability and improve the mean outcomes of psychotherapy. The assimilation model suggests that in time-limited treatments, clients with well-assimilated problems would do better in cognitive or behavioral therapies than in psychodynamic, experiential, or interpersonal therapies, whereas the reverse should be the case for clients with poorly assimilated problems. Results for high-, moderate-, and low-assimilation subgroups (based on rating the level of assimilation of problems presented in the first 20 min of first sessions) of clients (N = 112) randomly assigned to time-limited cognitive-behavioral or psychodynamic-interpersonal treatment supported the first suggestion but not the second (clients with poorly assimilated problems did equally well in both treatments).