Relationship of clinical features with psychological status in primary fibromyalgia. Clinical features and psychological status determined by the Minnesota Multiphasic Personality Inventory (MMPI) in 103 patients with primary fibromyalgia syndrome (PFS) were analyzed by univariate and multivariate techniques to determine if clinical features were related to psychological status or were intrinsic to PFS per se. The central features of PFS, e.g., number of pain sites, number of tender points, fatigue, and poor sleep, were independent of psychological status. However, discriminant analysis identified 4 variables--patient-reported depression, anxiety, stress, and pain severity--which together predicted 3 MMPI subgroups with an accuracy of 55% (P less than 0.001); the only musculoskeletal feature--pain severity--alone provided an accuracy of only 34% (P greater than 0.05). These data suggest a new concept, that the central features of fibromyalgia are independent of the psychological status and are more likely related to the PFS itself. However, pain severity may be influenced by psychological factors. 