Generalizations of prognosis with regard to insulin-dependent diabetes (IDDM) in epidemiological statistics are impaired not only by great intraindividual variations, but also due to methodical difficulties. Due to recent prognostic studies IDDM, particular in young age, must be considered as a rather serious disease with a 5 to 10 fold higher excess mortality in comparison with the general population. There are only few exact data about the extent of life shortening. Age of onset represents the most significant factor in life shortening. The younger the patient is at the age of onset the shorter he lives. From about 70 years onward diabetes has little or no effect on longevity. Whether the prognosis of IDDM has improved within the last decades remains uncertain. Long-term studies clearly indicate that IDDM is compatible also with a long life in a good health. Why many diabetics develop life shortening complications and why some patients do not cannot be answered with conclusive evidence.