BACKGROUND: Obesity, particularly morbid obesity, has various physical and mental complications. Excessive daytime somnolence (EDS) is a sleep disorder that reduces individuals' performance capability and the accuracy of their short-term memory and causes learning problems. This retrospective study aimed to document the presence of EDS in a sample of obese patients in comparison to patients with a normal weight. OBJECTIVES: This article compares the excessive daytime sleepiness of obese and non-obese patients in the minimally invasive surgery research center in Tehran, Iran. PATIENTS AND METHODS: In this case-control study, we compared excessive daytime sleepiness in 55 obese patients who were candidates for laparoscopic surgery, with a body mass index (BMI) of equal to or greater than 30 kg/ m2, with 55 controls with a normal BMI (19.5 - 24.9 kg/ m2). The process of selecting the control group in our case-control study is matching in group levels, so that the controls are similar to the case group with regard to certain key characteristics, such as age, sex, and race. The sleep assessment was based on the Epworth sleepiness scale (ESS) questionnaire. Analysis of variance (ANOVA) was used to compare the means of quantitative data, such as the ESS score of groups. RESULTS: Sleepiness was not affected by gender in cases or controls. The sleepiness prevalence was 29 (52.7%) in the cases group and 17 (30.9%) in the control group (OR = 2.493 (95% CI 1.144 -5.435)). The mean ESS scores in cases and controls were 7.82 ± 3.86 and 10.54 ± 6.15, respectively (P = 0.007). Moreover, the prevalence of sleepiness and the mean ESS scores in class III of obesity differed significantly from the controls (16 (57.1%) vs. 17 (30.9%)) (OR = 2.980 (95% CI 1.162 - 7.645)) and (11.04 ± 5.93 vs. 7.82 ± 3.86) (P = 0.013), respectively. CONCLUSIONS: Our findings suggest a strong relationship between EDS and obesity, particularly morbid obesity. Therefore, physicians must be familiar with EDS as a mixed clinical entity indicating careful assessment and specific treatment planning.