Background: Obstructive sleep apnoea (OSA) is highly prevalent in obese adults and independently linked to metabolic disturbances. Our study aimed to determine demographic and clinical differences in morbidly obese patients with severe OSA and those without OSA. Methods: Data was obtained from the Heart of England trust database for 56 morbidly obese (BMI≥40 kg/m 2 ) adults with polysomnographically-established severe OSA (apnoea hypopnea index-AHI≥30 events/hour; n = 30) or no OSA (AHI < 5 events/hour; n = 26). Age, sex, ethnicity, BMI, prevalence of type 2 diabetes (T2DM), HbA1c (DCCT-aligned), and bariatric surgery intervention were compared between the two subgroups at baseline and at 12–18 month follow-up. Results: Compared to non-OSA adults, OSA patients were older (P = 0.005) and more obese (P = 0.025), with trends towards a higher prevalence of T2DM (P = 0.054) and male sex (P = 0.073). The presence of T2DM was associated with older age (P = 0.008), male sex (P = 0.041), and lower minimum oxygen saturation (P = 0.033) in the entire cohort. Follow-up HbA1c values were improved [6.7(6–7.8) vs. 6.6(5.9-7.2)%; P = 0.028] in T2DM patients with treated OSA. There was no significant difference but greater variability in follow-up decrease in HbA1c in OSA T2DM patients on ventilatory treatment who underwent bariatric surgery than in controls without surgical intervention [−0.9 ± 1.15 vs. −1.1 ± 0.27%; P = 0.038]. Conclusion: Obesity, age, and male sex are important risk factors for OSA, even in a morbidly obese population. Complex management of OSA and obesity is associated with improved T2DM control. The greater variability in follow-up HbA1c in T2DM patients undergoing weight-loss surgery highlights the need for improved guidelines for T2DM management after bariatric surgery.