Purpose: This study aimed to investigate the influence of the thickness of the sinus lateral wall on the incidence of sinus membrane perforation. Materials and methods: A retrospective study was conducted by reviewing dental records of patients who received lateral wall sinus elevation in two educational institutes. The wall thickness 4 mm and 6 mm coronal to the sinus floor was measured with CBCT. The occurrence of sinus membrane perforation was recorded and correlated to the wall thickness using a multilevel regression analysis. Results: A total of 209 CBCT scans and patient records (N = 251 sinuses, with 42 scans exhibiting bilateral sinuses) were included. The mean residual ridge height was 3.33 ±1.41 mm. Sinus membrane perforation occurred in 67 sites. The overall mean lateral wall thickness was 1.59 ± 0.84 mm and 1.58 ± 0.83 mm at 4 mm and 6 mm coronal to the sinus floor, respectively. The mean wall thickness at 4 mm and 6 mm coronal to the sinus floor in the perforation group was 2.43 ± 0.56 mm and 2.41 ± 0.56 mm respectively, compared to 1.21 ± 0.40 mm and 1.23 ±0.41 mm respectively in the non-perforation group (P <0.01). The perforation rate was 56.4% if the lateral wall thickness at 4 mm coronal to the sinus floor was > 2 mm and 12.1% if it was < 1 mm. A similar difference in perforation rate was reported for the wall thickness measured at 6 mm coronal to the sinus floor (57.9% vs 13.4%). There was no statistically significant difference between smokers and non-smokers regarding perforation rate (P = 0.9604). The presence of sinus septa and sinus wall irregularities did not display a statistically significant difference (P = 0.7155 and P = 0.2971, respectively). Conclusion: The thickness of the lateral wall of the maxillary sinus was related to the occurrence of membrane perforation.