Intrauterine pregnancy after superovulation with gonadotrophins and after in-vitro fertilization (IVF) and embryo replacement has not been reported to occur in cases where the thickness of the pre-ovulatory endometrium was <6 mm. We report a case where an intrauterine pregnancy was established where the endometrium was no more than 4 mm in thickness at the time of follicular aspiration. It is suggested that an IVF cycle should not necessarily be abandoned merely because the pre-ovulatory endometrium is thin, and especially if other parameters, including follicular development and serum oestradiol concentrations, are appropriate.