Background: Our aim was to determine the effect of single endometriomas ≤3 cm in diameter per se on ovarian reserve in intracytoplasmic sperm injection (ICSI) cycles. Methods: We enrolled 19 consecutive infertile patients (29 cycles) who had unilateral single endometriomas ≤3 cm in diameter and who underwent ICSI. Results: The mean age of the patients was 33.3 ± 4.9 years. The mean diameter of endometriomas was 21.8 ± 4.9 mm. Left- and right-sided endometriomas were 34.5 and 65.5%, respectively. The number of oocytes retrieved from ovaries with endometriomas and contralateral normal ovaries was comparable (5.9 ± 4.3 vs. 5.4 ± 3.8). Conclusion: Endometriomas ≤3 cm in diameter per se did not have a deleterious effect on ovarian reserve in ICSI cycles.