Abstracy Background: Vitamin D has anti-inflammatory effects and has a modulation role in the immune system. In several studies, the role of vitamin D deficiency has been proven in respiratory and middle ear infection Aim: Study the effects of serum levels of vitamin D on the development of secretory otitis media and the adenoid hypertrophy. Patients and methods: This prospective case control study included a total of 150 subjects, who were divided into two groups; cases group which included 100 cases diagnosed with secretory otitis media and adenoid hypertrophy, and control group which included 50 healthy children. All 29 30 cases and controls were subjected to complete history taking, thorough ENT examination, and 31 32 tympanometry. In addition, serum vitamin D was ordered for all subjects. Results: The mean age of the study cases was 7.65 years, which significantly older than controls (mean age 6.1 – p = 0.002). However, no significant difference was detected between the two groups regarding gender (p = 1). The commonest season of presentation in the cases group was winter (70%), while the remaining cases presented at summer. The season of presentation was significantly different between the two groups (p = 0.017). Regarding vitamin D levels, it was significantly lower in the cases group (11.82 vs. 23.72 ng/ml in controls – p < 0.001). Using a cut-off value of 18.85, vitamin D had sensitivity and specificity of 100 and 90% respectively, with a diagnostic accuracy of 96.7%. All cases showed hypertrophied adenoids on X ray and type B tympanometry on tympanogram, while all controls showed normal sized adenoids in addition to type A tympanogram Conclusion: Our results suggest that low vitamin D levels are linked to both secretory otitis media with effusion together with enlarged adenoids. Therefore, measurement of the serum