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OBJECTIVE To identify the risk factors associated with dysmenorrhea in adenomyosis and to discuss the potential hormone-based understanding of pain mechanisms. STUDY DESIGN Adenomyosis patients with mild or no dysmenorrhea (n = 40, Group 1) and moderate-to-severe dysmenorrhea (n = 80, Group 2) were recruited. Charts of all patients were recorded. An immunohistochemistry (IHC) analysis was performed to detect the cellular levels of estrogen receptor-α (ER-α), estrogen receptor-β (ER-β), gonadotropin-releasing hormone receptor (GnRH-R), and neurofilaments (NFs) in 60 cases. RESULTS A history of cesarean section (CS) was positively related to the degree of dysmenorrhea in adenomyosis (OR (95% CI): 4.397 (1.371-14.104)). The ER-α levels in the eutopic endometrium (EUE) of Group 2 were higher than those in the ectopic endometrium (ECE) of Group 1. Group 2 had higher NF levels in the ECE than in the EUE. CONCLUSION A history of CS is a risk factor for adenomyosis with moderate-to-severe dysmenorrhea. For patients with adenomyosis, high ER-α levels in the EUE and high NF levels in the ECE may be related to moderate-to-severe dysmenorrhea. These hormone-based mechanisms may contribute to our understanding of the pathogenesis of dysmenorrhea in adenomyosis.