Endometriosis is characterized by endometrial tissue development outside the uterus. Anemia and iron depletion do not commonly accompany endometriosis in women, despite chronic abdominal inflammation and heavy menstrual bleeding. The objective of this study was to examine iron kinetics associated with endometriosis by using a NHP model, to better understand the underlying mechanism of abnormal hematogram values in women with endometriosis. Hematologic data from 46 macaques with endometriosis were examined for signs of iron depletion. Bone marrow, liver, and serum were used to elucidate whether iron loss or inflammation best explained the hematologic findings. Additional serum markers and intestinal biopsies from NHP with and without endometriosis were evaluated for patterns in iron kinetics across the menstrual cycle and for relative dietary iron-absorbing capacity. Almost half of the NHP with endometriosis were anemic. Overall, NHP had decreased RBC counts, increased MCV, increased percentage of reticulocytes, decreased serum hepcidin, and decreased hepatic and bone marrow iron. Intestinal expression of ferroportin 1, a mediator of iron absorption, was increased, indicating that despite high dietary iron, intestinal iron absorption did not compensate for iron losses. We concluded that use of oral iron supplementation alone does not replenish iron stores in endometriosis. Consequently, iron stores should be evaluated in women with endometriosis, even without overt clinical signs of anemia.