The Minnesota Multiphasic Personality Inventory (MMPI) profiles of 205 male and 157 female patients with acute and chronic low back pain (LBP) were studied for replicable homogeneous subgroups using three cluster-analysis procedures. Two normal and three clinically elevated profile subgroups were identified. The two normal subgroups were characterized by relatively normal musculoskeletal condition and were least disabled, but they differed somewhat from each other in duration of pain, presence of physical abnormalities, and daily functioning. The third subgroup had the following characteristics: an elevated neurotic triad, greatest duration of symptoms, most abnormal physical findings, greatest limitation of motion, most pain complaints during physical examination, and the fewest number of intact functional activities. The fourth subgroup, with an elevated neurotic triad plus subclinical elevations on other scales, had somewhat less musculoskeletal impairment but had extensive work disability, financial compensation, and previous surgeries. The fifth and most pathologic profile subgroup surprisingly consisted largely of acute-pain patients whose musculoskeletal condition and daily functioning were similar to those of the normal subgroups. Patients in the three abnormal MMPI subgroups were exposed to more LBP physical-risk factors in the workplace. Implications for psychological treatment with these different profile types are discussed.