Despite the fact that the McGill Pain Questionnaire (MPQ) is a useful pain assessment tool with widespread acceptance, empirical analyses have questioned its validity because they have not consistently supported the three a priori factors that guided its construction. The Spanish version that has followed the most systematic and rigorous reconstruction process (Lázaro C, Bosch F, Torrubia R, Banos JE. The development of a Spanish Questionnaire for assessing pain: preliminary data concerning reliability and validity. Eur J Psychol Assess, 1994;10:145-151) lacks evidence to support its construct validity. In the present study, the internal structure of the Spanish version of the McGill Pain Questionnaire (Lázaro C, Bosch F, Torrubia R, Banos JE. The development of a Spanish Questionnaire for assessing pain: preliminary data concerning reliability and validity. Eur J Psychol Assess, 1994;10:145-151) was examined in a sample of 202 acute pain patients and 207 chronic pain patients. Confirmatory factor analyses were carried out to compare alternative models postulating different internal structures (one-factor model, the classic three-factor model, and the semantic model inspired by the alternative structure found by Donaldson in 1995 (Donaldson GW. The factorial structure and stability of the McGill Pain Questionnaire in patients experiencing oral mucositis following bone marrow transplantation. Pain 1995;62:101-109)). Results from the LISREL CFA analysis indicated that the semantic model fitted better than the other models. On the other hand, intercorrelations between scales were smaller than the reliability indexes. In relation to concurrent evidence, significant correlations (0.001) were found between each subscale and the criteria measurements of every pain dimension. Only the affective subscale presented discriminant validity. Evidence supports the validity of the affective and sensory subscales but not the evaluative scale.