Obesity hypoventilation syndrome (OHS) is an important comorbidity in patients with obstructive sleep apnea (OSA). There is a paucity of data from India on this. We retrospectively studied consecutive patients who underwent a sleep study for suspicion of OSA, from January to July 2022. OHS diagnostic criteria was applied to all. Other data were extracted from electronic medical records. In all, 300 patients underwent a sleep study. 21 did not have OSA, though one was found to have OHS. In addition, 16 were excluded due to the non-availability of ABG, despite BMI ? 30 kg/m². Eventually, 263 were included in the analysis. Their mean age was 53 (12) and over two third (69%) were males. The prevalence of OHS in OSA was 6.8% (18/263). The mean BMI (37 vs 31), AHI (57 vs 34), and pH (7.38 vs 7.41) were significantly higher in the OHS group and FVC was significantly lower in the OHS group (58% vs 72%). Age and serum bicarbonate levels were not different between the two groups. In the bivariate analysis, the significant (p<0.05) predictors of OHS were female gender (OR 9.2; 95% CI 2.9 ? 29.2), headache (OR 2.8; 95% CI 1 ? 8.6), hypothyroidism (OR 3.37; 95% CI 1.2 - 9.2) and Diabetes Mellitus (OR 2.5; 95% CI 1 ? 6.7). The presence of orthopnea (OR 7.1), paroxysmal nocturnal dyspnea (OR 7.1) and nocturia (OR 3.2) had a trend towards predicting OHS. Multiple logistic regression identified female gender (OR 7.6; 95% CI 2.2 ? 26.1) to be the only independent predictor of OHS. To conclude, OHS is present in a small subset of patients with OSA. Apart from increased BMI, one needs to screen female OSA patients for OHS. Larger studies are warranted.