An exploratory investigation of behavioral treatment response during inpatient rehabilitation for severe mental illness is presented. Archival data from 26 weeks of behavioral contingency management (CM) programs targeting treatment nonadherence for 2 cohorts of participants were analyzed. For cohort 1 (N = 39), a multivariate analysis of longitudinal behavioral data identified 4 qualitatively and quantitatively distinct patterns of CM response and these groups differed in verbal memory ability. Analysis of cohort 2 (N = 45) replicated the finding of 4 patterns of CM response. We further clarified behavioral heterogeneity in cohort 2 by using hierarchical linear modeling with neurocognitive and social cognitive covariates. Results indicated that memory, attention, and a high external locus of control (LOC) were associated with level of nonadherence at baseline. Reductions in external locus of control were associated with greater CM response during the course of rehabilitation. Implications for understanding individual responses to the rehabilitation process are discussed.