Objectives To determine the psychopathological profile of patients with central sensitization (CS) in a sample of knee osteoarthritis, with and without CS, and fibromyalgia, and to compare their psychopathological profiles. Methods The final sample consists of 19 patients with osteoarthritis and CS (mean 66.37 years ± 8.77), 41 osteoarthritis patients without CS (mean 66.8 ± 7.39 years), 47 fibromyalgia patients (mean 46.47 years ± 7.92) and 26 control subjects (mean 51.56 years ± 11.41). The psychopathological profile was evaluated with the Millon Multiaxial Clinical Inventory. Results The average score of MCMI-III reflect higher scores in the fibromyalgia and osteoarthritis-CS groups. Patients with osteoarthritis-CS are more likely to report larger scores in Borderline and Major Depression scales. Fibromyalgia patients are more likely to report more increased scores in Somatoform and Major Depression, versus osteoarthritis-CS group. Fibromyalgia patients versus osteoarthritis without CS are more likely to report higher scores in Schizoid, Depression, Histrionic, Sadistic, Borderline, Somatoform, Posttraumatic Stress Disorder and Major Depression scales. Discussion Patients with CS have less differences in their psychopathological profiles as well as in both osteoarthritis groups and greatest differences are obtained between the fibromyalgia and osteoarthritis without CS, so perhaps presence of CS is the key to differentiate those groups and not chronic pain. An exhaustive assessment brings more accurate psychopathological profiles, thus better psychological treatment could be applied.