Objective No published studies have analyzed the possible link between vitamin D receptor (VDR) gene FokI polymorphism and obstructive sleep apnea (OSA). To better highlight this knowledge gap, we conducted this study to assess the linkage between VDR gene FokI polymorphism with OSA as a main objective and to assess the vitamin D (VD) level in patients with OSA, with stress on its severity subtypes. Patients and method A total of 240 patients with OSA and 120 matched controls were enrolled. All participants were subjected to full history taking, particularly sleep-disordered breathing symptoms, Epworth Sleepiness Scale assessment, measurement of serum VD, and assessment of FokI VDR gene polymorphism. Results OSA had a lower VD than controls (21.44±5.56 vs. 35.63±8.5, P<0.001). Moreover, 80% of controls had optimal VD status, whereas in OSA, 47.5% had VD deficiency. There was an indirect correlation between VD level and OSA severity (P<0.001). In OSA, the frequencies of ff, Ff, and FF genotypes were 42.2, 40.0, and 18.8%, respectively, and in controls were 50.0, 40.0, and 10%, respectively. There was an increased risk of OSA with the Ff (odds ratio=2.66, P<0.03), and the ff had a highly significant association with an increased risk of OSA (odds ratio=10.59, P<0.001). Conclusion This work introduces for the first time a possible association between VDR gene FokI polymorphism and Egyptian population with OSA. Lower VD was significantly observed in OSA and correlates with disease severity.