Estimates of the cost of Type 1 (insulin-dependent) diabetes mellitus should take into account the development of various complications. In this study, we calculated separately the basic direct costs of a Type 1 diabetic patient over a span of 35 years of living with the disease, and on average, the cost of complications which developed during this period of time. Assessment of costs showed that there is a difference between the cost of treating the disease itself, which decreases over the years, and the cost of treating its complications, which increases. The cost of treating one patient over the 35-year period amounted to about 247,000 pounds in 1993 prices, and in terms of discount value, to about 104,000 pounds. These costs are significant in planning the health expenditure and the investment of resources for prevention of the disease, and in selecting proper methods of treatment of complications.