子宫腺肌症（英语：Adenomyosis），是指子宫内膜侵入子宫肌层引起的一种良性病变，以往又称之为内在性子宫内膜异位症。临床以继发性加重的痛经，月经量增多或经期延长，子宫增大为主要表现。本病多发于35-50岁妇女。经报道，妇科手术切除的子宫标本中，6%-40%有子宫腺肌症；有10%左右患者并存子宫内膜异位症，约三分之一并有子宫肌瘤。

此病发病原因及机制，目前尚未明确。通常认为是子宫内膜基底层直接向肌层浸润的结果。一些因素包括有：创伤，如多次妊娠与分娩，或宫腔手术，导致子宫壁损伤，从而有利于部分子宫内膜向肌层生长。二是卵巢功能失调，持续高水平雌激素刺激，破坏子宫肌层的防御能力，促使子宫内膜向肌层生长。此外，少数位于深肌层的孤立病灶，可能是子宫内膜碎片经血管或淋巴管扩散所致。

Adenomyosis is a medical condition characterized by the presence of ectopic glandular tissue found in the muscular wall of the uterus (myometria). The term adenomyosis is derived from the Greek terms adeno- (meaning gland), myo- (meaning muscle), and -osis (meaning condition). Previously named as endometriosis interna, but adenomyosis differs from endometriosis and these two diseases represent two separate entities. They are found together in many cases.