Abstract： Objective To investigate nerve fibers distribution in endometrium of adenomyosis and their relationship with dysmenorrhea. Methods Endometrial tissue was sampled from 74 hysterectomy specimens including 32 cases with adenomyosis and 42 cases with uterine fibroids. Two-step Envision immunohistochemical staining was used to detect distribution of nerve fibers in endometrium. Highly specific polyclonal rabbit anti-protein gene product 9.5 (PGP9.5) and monoclonal mouse anti-neurofilament protein (NF) were used to demonstrate both myelinated and unmyelinated nerve fibers in endometrium in women with adenomyosis and uterine fibroids. Results The positive rate of PGP9.5 immunoreactive nerve fibers in the functional layer of endometrium of pain patients were with 64%(14/22) in adenomyosis and 67% (10/15) in uterine fibroids. And their density were 0.6(0-9.4)/mm2 and 0.6(0-6.0)/mm2 without reaching statistical difference (P> 0.05). No expression of NF could be detected in the functional layer of endometrium of adenomyosis and uterine fibroids. There were no PGP9.5 immunoreactive nerve fibers in the functional layer of endometrium in non-pain women with adenomyosis and uterine fibroids. Moreover, No NF immunoreactive nerve fibers in the functional layer of endometrium were shown in non-pain patients with adenomyosis and uterine fibroids. PGP9.5 immunoreactive nerve fibers and the nerve density in the basal layer of endometrium were 64%(14/22), 1.1(0-12.0)/mm2 in pain adenomyosis and 50%(5/10), 0.6(0-3.0)/mm2 in non-pain adenomyosis. NF immunoreactive nerve fibers and the density in the basal layer of endometrium were 23%(5/22),(0-0.6)/mm2 in pain adenomyosis and 20% (2/10),(0-1.0)/mm2 in non-pain adenomyosis. PGP9.5 immunoreactive nerve non-pain fibroids. NF immunoreactive nerve fibers and the nerve density in the basal layer of endometrium were 40%(6/15),0(0-0.4)/mm2 in pain fibroids and 15%(4/27),0(0-1.0)/mm2 in non-pain fibroids. There was no statistical different PGP9.5 and NF immunoreactive nerve fibers distribution in basal layer of endometrium between pain adenomyosis and pain fibroids or between non-pain adenomyosis and non-pain fibroids (all P>0.05). However, PGP9.5 immunoreactive nerve fibers density in basal layer of endometrium was higher in pain adenomyosis and fibroids when compared with non-pain adenomyosis and fibroids(P<0.05). Conclusions PGP9.5 immunoreactive nerve fibers might confer the occurrence of pelvic pain, however, NF immunoreactive nerve fibers may not involved in the pathogenesis of pain.