Classifying clients with serious and persistent mental illness (SPMI) into groups with differential demographic and clinical characteristics that relate directly to the need and receipt of services and changes in functioning provides a strong foundation on which to build program- or system-level planning, development, and evaluation efforts. In this study, clinician-generated problem data and cluster-analytic techniques were used to develop a four-group typology for a sample of 293 clients with SPMI. Each of the types--extremely disabled, young adult, personally distressed, and adapted--was profiled demographically and clinically in terms of human service needs, prognosis, and treatment outcomes. Each of the four types evidenced a unique pattern of needs and outcomes that was consistent with its clinical profiles. The typology, associated service needs, and outcomes provide valuable information for use in service planning and program development for clients with SPMI.