Vitamin D deficiency and asthma are common public health problems worldwide. Recently, newer physiologic functions for vitamin D have been identified. Several studies suggest vitamin D plays a vital and complex role in immune system function and regulation. Asthma is one of the most common chronic diseases worldwide and has been increasing in prevalence over the last decades. Common risk factors for both asthma and vitamin D deficiency, such as an urbanized, westernized lifestyle and obesity have led to a hypothesized link between asthma and vitamin D. The purpose of this review is to present the evidence for a role of vitamin D in asthma.