Since its introduction in 1922, insulin therapy has undergone constant development and improvement. Today, the spectrum ranges from short- to very long-acting depot insulins, and "human" insulins. Further stages in the development of this form of treatment have been intensive insulin therapy, self-measurement of blood sugar, development of insulin-analogues and the use of insulin pumps or pens, to mention but a few. As a reflection of how widespread insulin therapy in the doctor's office has become and what the frontiers are, the present paper lists a range of 15 errors, and discusses how they can be avoided and insulin treatment thus further optimized.