AIM: To determine the influence of gaps [places where neither the donor’s nor the recipient’s Descemet’s membrane (DM) is present] and overlaps (places where the recipient’s DM is covered by the donor’s DM) on the frequency of postoperative detachment of DM endothelial keratoplasty (DMEK) lamellae. METHODS: Totally 64 eyes of 64 patients with Fuchs’ endothelial dystrophy or bullous keratopathy indicated for DMEK were randomly divided in two groups. The diameter of the implanted DMEK lamella was the same in both groups (8 mm), but we changed the diameter of the removed recipient DM. In the first group (32 eyes), the circular area was approximately 8.5 mm (gaps); in the second group (32 eyes), the diameter was 7.5 mm (overlaps). Postoperatively we noted all cases of detachment visible on the slit lamp and these cases we indicated for rebubbling. We also measured the uncorrected distance visual acuity (UDVA) as well as corrected distance visual acuity (CDVA) in decimal and postoperative endothelial cell density (ECD). The minimum follow-up time was 6mo. RESULTS: The number of rebubbling procedures in the entire group of patients was 13, i.e., 20.3%, with 6 eyes (18.7%) in the gap group, and 7 eyes (21.9%) in the overlap group. Lamella replacement (re-DMEK) was required in 3 (gap group) and 2 patients (overlap group), respectively. The difference between the groups was statistically insignificant. The UDVA was 0.54±0.21 in the gap group and 0.58±0.24 in the overlap group. The CDVA was 0.74±0.22 and 0.80±0.16, respectively. ECD was 1920±491 and 2149±570 cells/mm2. The small differences between both groups were not statistically significant. CONCLUSION: We do not notice any difference in the group of patients with overlaps or gaps of DM. The presence of small areas of gaps or overlaps does not affect the frequency of detachment of the DMEK lamellae.