The relationship between vitamin D and the skin starts with the synthesis of vitamin D in the skin. New mechanisms on how the most researched vitamin affects the biggest organ in the human body are constantly investigated and observed. The aim is to review the current knowledge on vitamin D and skin interaction, as well as the effect of vitamin D levels on skin diseases. According to some studies, suboptimal vitamin D levels are found in as many as 30 – 90% of the population, with an estimated vitamin D insufficiency in about one billion people worldwide. In 25.6 – 68% of patients with psoriasis, there is a deficiency of vitamin D and insufficiency of vitamin D in as many as 97% of patients. Furthermore, a series of observational studies and meta-analyses have shown that the serum levels of calcidiol are lower in children and adults with atopic dermatitis, and some studies have shown that up to 70.5% of patients with vitiligo have vitamin D deficiency. Low levels of vitamin D are associated with the progression of malignant melanoma, but it is unknown at which point UV exposure ceases to be protective through vitamin D and begins to be a risk factor for the development of skin tumours. Despite many studies that have been conducted, the nature of the relationship between vitamin D and certain skin diseases is still unknown, whether it is causal or accidental, while in others, such as psoriasis, evidence of the correlation with vitamin D levels is used in daily work with patients – in diagnosis and treatment.