Obesity is a chronic metabolic disease that affects an increasing number of people around the world. There have been limited studies evaluating the weight loss effects of orlistat in the Korean population, whose diet is different from that of the Caucasian population. The primary objective of this study was to evaluate the effect of orlistat on the weight and body mass index of obese and overweight Korean patients. The secondary objective was to evaluate the effects of orlistat on risk factors for obesity and metabolic disorders. Obese adult patients with a body mass index greater than 25 kg/m(2) who received 120 mg of orlistat three times daily for 24 weeks were included in this study. Patients were retrospectively evaluated for changes in body weight and body mass index, as well as waist and hip circumference, body fat levels, serum lipid levels, fasting glucose levels, and blood pressure. The evaluation included 63 patients. Treatment with orlistat for 4, 12, or 24 weeks significantly decreased the weight, body mass index, waist circumference, and hip circumference compared to that at the baseline. The average weight loss was 3.0 kg at 12 weeks and 3.6 kg at 24 weeks, which indicated a 3.8 and 4.6 % decrease from initial weight, respectively. The number of patients who lost more than 10 % of their initial body weight was 3 (4.8 %) at 12 weeks and 27 (7.9 %) at 24 weeks. About 27 % of patients reported gastrointestinal-related adverse effects with orlistat, but no serious adverse effects were reported. A retrospective study of overweight and obese Korean patients showed that treatment with orlistat for 24 weeks significantly decreased body weight and body mass index compared to the initial weight.