Renal insufficiency is a common disease, in the general population as well as in some specific diseases such as HIV infection or cancer. The vast majority of medicines require a dosage adjustment in case of renal dysfunction, it is thus of a crucial importance to know how to evaluate appropriately renal function, on one hand, but also to have access to reliable information sources on how to handle the drugs in such cases. Most often, the Summary of Drug Characteristics (SmPC) only provides partial information, which may even be false in some cases as compared to the most recent data from the literature. However, some information sources exist, reliable, updated, and easily accessible.