SYNOPSISThis study attempts to replicate and synthesize previous headache/MMPI research by investigating scale differences amongst diagnoses and between a control group; re-examining the occurrence of the conversion “V” pattern; evaluating the Kudrow-Sutkus (1979) classification system; measuring score changes which occur with prognosis; and observing the effect that “headache items” have on scale score elevations. Several mean scale scores differed from previous studies. A number of these differences were clinically significant. Analysis of variance (ANOVA) (sex [370 males and females] and headache diagnosis) for each scale determined that males had higher L scores; the control group had higher K scores than post trauma, mixed, or vascular patients; each headache diagnosis had higher 1, 2, 3, and 7 scores than the control group (scales 1, 2, and 3 were clinically elevated in only the post trauma and mixed conditions); scale 9 scores varied between conditions; and scale 10 scores were higher for migraine, mixed, cluster, and post trauma patients. Chi-square analysis determined that the conversion “;V” pattern occurred in a significantly greater degree in headache patients. However, the percentage of occurrence ranged from only 12.50 to 31.03 percent. The Kudrow-Sutkus system correctly diagnosed only 40.08 percent of 90 randomly selected subjects. One-way ANOVA determined that no significant change occurred in group scale scores in 20 headache sufferers who received treatment ranging from a multi-disciplinary hospital program to none at all and whose prognosis ranged from excellent to poor. One-way ANOVA determined that the removal of items which inquire about “headache symptoms” produced significant reductions on scales 1 and 3.The inability of this study to replicate previous empirical investigations raises questions of the MMPI's reliability as a diagnostic classifier in chronic headache. Certain elevations on the MMPI may be the result of symptom measurement and not psychopathology.