Background: In past years recreational diving has attracted more and more interest and among such divers an increasing number of diabetic divers. However, there is limited research on the accuracy of CGM systems under hyperbaric conditions and consistently diving guidelines make little reference to the use of CGM. Subject and Method: This exploratory study collected blood glucose samples of one diabetic diver over four dives and assessed the deviation of intersitial glucose values from two CGM systems based on 33 samples. A notable step of this method is to collect the data from actual dives under water. Results: The results indicate that a) under hyperbaric conditions of up to 2bar additional pressure and b) after decompression both CGM systems work comparably accurate as indictated by the manufacturer under normal conditions. This has been checked in terms of MARD and Clarke Error Grid Distirbution. Conculsion: For diabetic divers the results suggest they may take CGM monitors with them on dives to react to potential hypoglycemic events before they occur, i.e. when it is still safe to supplement glucose. For dive guidelines the results imply that these could reference CGM for dive planning and monitoring during the dive to increase divers‘ safety. For research this exploratory confirms the current hypothesis that neither increased pressure nor saltwater have an effect on blood glucose and the functioning of CGM systems. Further research may include additional sampling (number and depth) and more elaborate blood glucose measurement. The experimental setup applied is an efficient way to test further CGM systems.