Background: Chronic suppurative otitis media (CSOM) is a persistent inflammatory condition of the middle ear, frequently affecting children in low- and middle-income regions. Emerging evidence highlights the role of vitamin D in modulating immune function and reducing susceptibility to recurrent infections. This study aimed to assess the association between serum 25-hydroxyvitamin D [25(OH)D] levels, white blood cell (WBC) count, neutrophil-to-lymphocyte ratio (NLR), and clinical severity in children with CSOM. Methods: A case-control study was conducted from March to June 2025 across private ENT clinics in Kirkuk, Iraq. The study included 100 children aged 2–12 years, divided equally into CSOM cases and healthy controls. Diagnosis was confirmed by ENT specialists based on clinical and otoscopic findings. Serum 25(OH)D levels were measured using ELISA. Inflammatory markers including WBC count and NLR were assessed via complete blood count. Demographic, environmental, and clinical data were collected through structured interviews. Statistical analyses were performed using SPSS v25. Results: Vitamin D deficiency (<20 ng/mL) was significantly more frequent in CSOM patients (64.0%) compared to controls (28.0%) (p<0.001). Mean serum 25(OH)D levels were significantly lower in the CSOM group (18.2±6.1 ng/mL) than in controls (29.4±7.2 ng/mL). CSOM patients exhibited higher WBC (9.3±2.1 vs. 6.8±1.9 ×10³/µL), lower lymphocyte counts (2.1±0.6 vs. 2.7±0.7 ×10³/µL), and elevated NLR (2.95±0.84 vs. 1.26±0.56) (all p<0.001). A strong inverse correlation was observed between vitamin D levels and NLR in CSOM children (r = –0.61, p<0.001). Multivariate analysis identified vitamin D deficiency (OR: 3.45), low sunlight exposure (OR: 4.12), and elevated NLR (OR: 3.89) as significant predictors for CSOM. Conclusion: Children with CSOM demonstrated significantly lower vitamin D levels and elevated inflammatory markers compared to healthy controls. These findings suggest that vitamin D deficiency contributes to immune dysregulation and may increase the risk and severity of CSOM. Routine screening and correction of hypovitaminosis D could serve as an adjunctive strategy in managing pediatric CSOM.