Extended the MMPI cluster analysis to patients with heterogeneous chronic medical conditions by replicating prototypic MMPI cluster group profiles and by relating cluster groups to clinical baseline and outcome 263) of chronically ill = 254 and n = datSs were 2 independent samples (n patients admitted to an inpatient medicine/psychiatry unit. Using a 4-cluster solution, similar cluster profile groups were replicated in both samples. Consistent differences emerged between cluster groups on functional impairment, psychiatric diagnoses, depression, and psychosomatic symptoms. Cluster group membership also predicted changes in functional impairment and depression 6 mo after treatment. Results are discussed in terms of similarities between chronic low back pain and chronic illness and tailoring treatment to different patient types.