An idiographic procedure designed to assess the belief systems of criminal offenders is described, investigated, and clarified. This measure, the Cognitive Map of Major Belief Systems (CMMBS), assesses the five belief systems (self-view, world-view, past-view, present-view, future-view) held to occupy the higher echelons of human cognition. Modest to moderate test-retest reliability was achieved when 19 inmates, enrolled in one of three drug-counseling groups, completed the CMMBS on two separate occasions, 2 weeks apart. It was also ascertained that the drug treatment specialist who served as therapist for all three groups "blindly" matched the 19 CMMBS records to the inmates who produced them. A case study of one of the 19 participants was used to illustrate how the CMMBS is employed with individual offenders and how belief systems interact with major schematic subnetworks such as attributions, outcome expectancies, efficacy expectancies, goals, values, and thinking styles to create crime-supporting lifestyles.