BACKGROUND: Laparoscopic sleeve gastrectomy (LSG) has become a widely utilized surgical procedure for losing weight since its approval for insurance coverage in Japan in 2014. Its efficacy has been demonstrated by research, but data concerning gastric wall thickness following surgery remain unavailable. Hence, this study aimed to measure gastric wall thickness in resected, formalin-fixed specimens and explore the influence of obesity-related comorbidities on these measurements. METHODS: This prospective study included 53 patients undergoing bariatric surgery at Oita University Hospital. Full-layer thickness (FLT) and muscle-layer thickness (MLT) in the antrum, body, and fornix of resected gastric specimens were measured. Data on patient demographics, comorbidities, and surgical procedure were also collected and analyzed using JMP software. Furthermore, associations between gastric wall thickness and patient factors were assessed. RESULTS: The mean FLT in the antrum, body, and fornix was 2.9, 2.6, and 2.3 mm, with corresponding MLT of 1.2, 1.0, and 0.9 mm, respectively. The antrum exhibited the thickest gastric wall, whereas the fornix was the thinnest. Diabetes mellitus (DM) was associated with decreased MLT in the fornix, and obstructive sleep apnea (OSA) affected both FLT and MLT in the antrum. CONCLUSIONS: Comorbidities such as DM and OSA significantly influence gastric wall thickness, particularly in the antrum and fornix. Understanding these variations is critical for optimizing surgical techniques and selecting the right stapler in LSG.