Background Vitamin D deficiency has been proposed as a risk factors of cerebrovascular stroke. Objectives The aim of this study was firstly, to assess the serum level of vitamin D in cerebral stroke patients and secondly, to examine if its deficiency was associated with stroke severity and outcome. Methods We utilized a case-control study design and recruited 138 acute stroke patients and 138 age- and sex-matched controls from subjects attending outpatient clinic for other reasons. All participants were subjected to full general and neurological examination. Brain imaging CT and/or MRI was performed. Blood samples were collected for measurement of serum level of vitamin D (ng/ml) by ELISA, alkaline phosphatase, serum calcium, and phosphorous. The stroke severity was assessed by the National Institutes of Health Stroke Scale (NIHSS) and stroke outcome was assessed by modified Rankin Scale (mRS). Results Stroke patients had significant lower levels of vitamin D compared with the control group. Vitamin D deficiency remained significantly associated with the NIHSS stroke severity score and the mRS 3-month stroke outcome after controlling for other significant factors such as age, dyslipidemia, and infarction size using multivariable logistic regression analysis. Conclusion Our results demonstrated that stroke patients suffer from vitamin D deficiency, which was associated with both stroke severity and poor outcome. Vitamin D supplementation could exert a therapeutic role in the management of cerebral stroke.