A study was made of the personality profiles of a sample of 51 patients with chronic tension-type headache (CTH) employing the Minnesota Multiphasic Personality Inventory (MMPI). Two clusters were obtained by applying multivariate classification techniques: cluster 1 (with elevations on scales Hy, D and Hs only) and cluster 2 (exhibiting elevations on most scales except Pd, Mf and Si). Fifty subjects without chronic pain or known psychiatric disorders, and extracted from the same social setting as the patients, completed the MMPI as a control group. Fluoxetine treatment was started in the CTH group, with follow-up over a 1-year period. Chi-squared analysis correlating the clusters obtained to different pain-related variables and epidemiological parameters revealed a significant association to sex only. There were no differences in therapeutic response between the two clusters. However, the patients belonging to the less perturbed cluster who exhibited profiles analogous to those of the control population showed significant improvement with respect to the global sample and their own cluster.