Despite advances in the understanding of pain mechanisms and innovative strategies to assess pain patients, there continues to be a substantial proportion of patients who do not appear to benefit from treatment interventions available. One possible explanation for these results is the tendency to treat chronic pain patients as a homogeneous group with generic treatments--adherence to "patient and treatment uniformity myths." Following from the traditional medical model, several attempts have been made to identify specific subgroups of patients exclusively on the basis of physical factors. In addition, a number of studies have attempted to empirically identify subgroups of pain patients using standard psychiatric assessment instruments (e.g., MMPI, SCL-90) and, recently, cognitive measures and measures of pain behaviors. These different approaches and the assessment instruments used are reviewed, and the limitations are described. Alternative strategies to classify subgroups of pain patients based on combinations of physical, psychosocial, and behavioral measures (i.e., multiaxial strategies) are presented. The efforts to classify homogeneous subgroups of chronic pain patients are reviewed, and the potential utility of customizing therapeutic interventions to patient characteristics is discussed.