Objective: The presence of lymphatic vessels in endometrium has been controversial and recent immunocytochemical studies with routinely paraffin embedded sections revealed lymphatic vessels in basalis and occasionally in functionalis. We aimed to investigate endometrial lymphatic vessels by immunocytochemical staining using cryosections, which provided better and consistent immunostaining for lymphatic vessels with a lymphatic marker, D2-40. We aimed further to explore the structure-function relationship of lymphatic vessels in the menstrual cycle. Materials and Methods: Sixteen cases of endometrium from menstrual, early-proliferative to latesecretary phase were immunostained for D2-40 and lymphatic vessels were morphometrically analyzed for functionalis, basalis and myometrium, respectively. Results: Lymphatic vessels were consistently most numerous in myometrium, followed by basalis in all phases whereas menstrual endometrium showed small, fragmented aggregates of lymphatic vessels in thin basalis. Earlyto mid-secretary endometrium revealed many lymphatic vessels in basalis and lower-functionalis with few lymphatic vessels in upper-functionalis. Late-secretary endometrium revealed more lymphatic vessels in upper-functionalis with dilated walls, which then burst at the surface of functionalis. Conclusions: These degenerating lymphatic vessels with markedly dilated lumen in upper-functionalis may contribute to lymphatic leakage in late-secretary phase. These immunostained lymphatic vessels in functionalis support proliferating and degenerating lymphatic vessel cycle synchronized with the menstrual cycle of endometrial arteries to maintain adequate fluid leakage.