An increase in respiratory work load and resistance to respiration cause a decrease in respiratory muscle endurance (RME) in patients with obesity hypoventilation syndrome (OHS). We aimed to evaluate and compare RME in subjects with OHS and a control group using an incremental load test and compare the RME of subjects with OHS in whom noninvasive ventilation (NIV) was and was not used. Forty subjects with OHS (divided according to body mass index [BMI] as group I: 30-40 kg/m2; and group II: ≥ 40 kg/m2) and 20 subjects with obesity (control group: 30-40 kg/m2) were included in the study. RME was evaluated using the incremental load test, and respiratory muscle strength (RMS) was evaluated using mouth pressure measurements. The 6-min walk test, Epworth Sleepiness Scale (ESS), Pittsburgh Sleep Quality Index (PSQI), Fatigue Severity Scale (FSS), EQ-5D Health-Related Quality of Life Questionnaire (EQ-5D), and the Obesity and Weight-Loss Quality of Life Instrument (OWLQOL) were performed. RME and RMS (%) in group I were lower than the control group (P = .001, P = .005, and P = .001, respectively). No significant difference was found between the 3 groups in terms of 6-min walk distance (6MWD) percentage predicted values (P = .98). RME in the NIV user group was higher than the non-user group (P = .006). ESS, total PSQI, and FSS scores in the control group were less than group I (P = .01, P = .009, and P = .005, respectively) and group II (P = .01, P < .001, and P < .001, respectively). The EQ-5D scores of the control group were higher than group II only (P = .005 and P = .005, respectively). There were no differences in OWLQOL between the groups (P = .053). RME was low in subjects with OHS but higher in those who used NIV. The incremental load test could be performed easily and safely in a clinic setting.