Diabetes mellitus (DM) was previously considered a contraindication to recreational diving by means of self-contained underwater breathing apparatus (SCUBA), the main concern being the risk of the divers developing underwater hypoglycaemia. However, an increasing body of scientific evidence including epidemiologic surveys and controlled case studies have shown, that some patients with DM can dive safely under the right circumstances. In this review, we summarise the Danish national guidelines based on existing literature and guidelines as well as patient instructions on how to improve safety when diving with DM.