Background Bariatric surgery is being recognized increasingly as an effective treatment for obesity and related comorbidities. In Japan, the cost of laparoscopic sleeve gastrectomy (LSG) is covered by the national health insurance for adults with a body mass index (BMI) >= 35 kg/m(2)and specific comorbidities (type 2 diabetes mellitus (T2DM), hypertension (HT), dyslipidemia (DL), and obstructive sleep apnea syndrome (OSAS)). However, only 0.6% of the adult population have a BMI >= 35 kg/m(2). In contrast, 4.3% have class I obesity (a BMI of 30-34.9 kg/m(2)). The BMI of Asians with central obesity-induced diabetes and other metabolic disorders is much lower than that of Westerners. Objectives To evaluate the medium-term (up to 5 years) outcomes of LSG performed in Japanese patients with class I obesity. Methods One hundred eighteen consecutive patients with class I obesity treated by LSG at our center between August 2007 and December 2018 were included in a retrospective study. Mean preoperative body weight (BW) and BMI were 88.6 +/- 10.3 kg and 32.8 +/- 1.6 kg/m(2), respectively. Weight loss, comorbidity status, and adverse events were assessed. Results Mean BW/BMI at 1, 3, and 5 years after LSG decreased significantly to 66.6 +/- 11.2 kg/24.6 +/- 2.8 kg/m(2), 68.0 +/- 14.0 kg/25.4 +/- 4.0 kg/m(2), and 69.1 +/- 12.9 kg/26.5 +/- 3.0 kg/m(2), respectively. Mean total weight loss at 1, 3, and 5 years was 24.7 +/- 8.2%, 21.8 +/- 12.1%, and 18.5 +/- 9.7%, respectively. Metabolic disorders such as T2DM, HT, and DL improved significantly. There was no mortality. Conclusion LSG is safe, yields excellent weight loss, and improves obesity-related comorbidities in Japanese patients with class I obesity.