BACKGROUND: Vitamin D deficiency has been linked to various medical conditions such as bone loss, decreased mineralization, endocrine disorders, and central nervous system disorders, including epilepsy. Vitamin D deficiency is prevalent among patients with epilepsy (PWE). However, the specific association between vitamin D levels and age in PWE is unclear. OBJECTIVES: Identify the relation between vitamin D level and age in PWE and evaluate factors that may play a role in seizure control. DESIGN: Retrospective analytical medical record review SETTING: Outpatient epilepsy research clinic in Saudi Arabia PATIENTS AND METHODS: Between November 2016 and April 2020, we selected eligible PWE aged older than 14 years whose vita-min D levels were recorded at least once after reviewing 1550 patient electronic files. We analyzed data on serum vitamin D level by age and other factors, vitamin D supplement use, seizure classification, and conducted a multivariate logistic regression to assess associations with seizure control. MAIN OUTCOME MEASURES: Relationships between vitamin D levels and age and factors that might affect seizure control. SAMPLE SIZE: 524 patients RESULTS: The prevalence of low serum vitamin D levels was high (86.8%). The median vitamin D level in all patients was low (38 nmol/L), and was lower in young PWE than in adult PWE ( P <.01). Only 146 patients received vitamin D supplements. High vitamin D levels were associated with a 40% seizure reduction. CONCLUSION: Vitamin D deficiency is underestimated in PWE in Saudi Arabia, and is more prevalent among young adults and patients on polytherapy than in other PWE. Patients with high vitamin D levels had good seizure control compared with those with low levels. The effect of vitamin D supplements on seizure control should be further investigated in randomized control trials. LIMITATIONS: Retrospective study and no categorization by presence of supplementation. CONFLICT OF INTEREST: None.