Purpose: To report the second case of successful conception in a natural cycle despite a maximum endometrial thickness in the late follicular phase of four mm. Materials and Methods: A 31-year-old woman with short term infertility was evaluated for follicular endometrial maturation with pelvic sonography. Results: She was treated with progesterone in the luteal phase. Despite attaining a very good serum estradiol and having a longer follicular phase (with then more time of estrogen exposure to increase the endometrial thickness) she conceived in this cycle of investigation. Conclusions: Reporting a successful second case makes it less likely that the first case was a miracle. The odds are that there have been other pregnancies with four-mm endometrial thickness in natural cycles without follicle maturing drugs that have either not been reported, or more likely, not evaluated.