Aims: Following the identification of endometrial intravascular thrombi (IVT) as the presenting feature in a patient with antiphospholipid syndrome, additional biopsy specimens were reviewed to determine the frequency and histological associations of IVT in the endometrium. Methods and Results: Eighty-five additional biopsies were reviewed including 44 consecutive cases demonstrating shedding changes (both menstrual and non-cyclical), 30 cases without shedding (normal and non-cyclical), and 11 cases in which unusually prominent IVT had been recorded upon initial histological assessment. In the shedding group, IVT were significantly more common in biopsies showing disordered proliferative endometrium (DPE, 4/7 cases) than normal menstrual appearances (4/22 cases), and organising vascular changes were seen only in the former. IVT in DPE cases were also commonly multifocal and sometimes involved abnormal ectatic vessels. None of the 30 non-shedding cases demonstrated IVT. Eight of the 11 biopsies with prominent IVT demonstrated DPE and shedding but three cases demonstrated otherwise normal cyclical appearances. Conclusions: IVT may be seen occasionally in normal menstrual endometrium but are more characteristic of DPE, and organising vascular changes are suggestive of abnormal haemostasis. An underlying thrombotic disorder may be considered when endometrial IVT occur in the absence of shedding changes.