Measurement of endometrial thickness by vaginal ultrasonography is used to detect post-menopausal women at risk for endometrial pathology. The efficacy of this procedure is doubtful in cases of intrauterine fluid accumulation, which is a common finding in this population. We present a case of endometrial carcinoma in an asymptomatic, post-menopausal woman with ultrasonographic imaging of an atrophic endometrium and intra-cavitary fluid. It may be suggested that, in a case of intrauterine fluid accumulation (IFA), endometrial biopsy should be performed regardless of the sonographic endometrial thickness, since the fluid may increase the intracavity pressure and can mask endometrial pathology. (C) 1998 Elsevier Science Ireland Ltd.