Purpose: To determine if successful pregnancies are possible following fresh or frozen embryo transfer despite a maximal endometrial thickness of only < 5 mm. Methods: A retrospective review of all fresh and frozen embryo transfers over a seven-year period was performed. The maximum thickness either on the day of human chorionic gonadotropin injection during fresh embryo transfer or the day before the initiation of progesterone in frozen embryo transfer was performed. All embryo transfers performed with a maximum endometrial thickness of 5 mm were identified and the pregnancy rates were determined. Results: There were 35 embryo transfers performed with a maximum endometrial thickness of < 6 mm. There were three clinical pregnancies (8.5% per transfer), two live delivered babies (5.7% pregnancy rates per transfer). One of the live births was a fresh transfer using a minimal stimulation protocol and the endometrial thickness was 5.8 mm and the other a frozen embryo transfer with a maximum thickness of 5.0 mm (1 of 7, 14.2% of frozen embryo transfers resulted in a live delivery despite thin endometria. Conclusions: Live delivered pregnancies are possible despite thin endometria but the pregnancy rate is poor. Possibly the pregnancy rates may be better without controlled ovarian hyperstimulation.