OBJECTIVE:The aim of this study was to investigate the association between comorbidities and chronic diseases and neuropathic and nonneuropathic orofacial pain diagnoses to suggest subclassifications of disease. STUDY DESIGN:This was a cross-sectional, retrospective, case-control study. We evaluated 174 patients with orofacial pain and 132 controls by using a systematic protocol that consisted of medical history and demographic, pain, and orofacial characteristics. Patients were grouped according to their diagnosis-neuropathic or non-neuropathic pain; medical comorbidities; and exclusion criteria. Analyses included Z-score normalization, χ2 test, Fisher's exact test, 1-way analysis of variance (ANOVA), Student t test, Pearson's correlation coefficient, 2-step clustering, and logistic regression at 95% confidence level. RESULTS:Functional chronic diseases were prevalent and correlated with pain and orofacial features. Three groups were identified in the cluster analysis: neuropathic facial pain, other orofacial pain syndromes, and fibromyalgia/temporomandibular disorders (TMDs). Logistic regression showed that hypothyroidism and gastritis were predictors for nonneuropathic orofacial conditions. Psychiatric diseases and gastritis were more prevalent among patients with generalized pain syndromes and TMDs and less prevalent among patients with neuropathic pain. CONCLUSIONS:Functional comorbidities were associated with orofacial and dental features and may correspond to multimorbidity states in patients with chronic orofacial pain. The findings support the hypothesis that nonneuropathic orofacial pain syndromes could be functional disorders.