Prevention and control programmes are needed to stem the rising epidemic of diabetes and its complications. However, these will not occur unless governments and public health planners are aware of the potential problem. Using published prevalence rates for NIDDM in different populations, and the current and projected age distributions, worldwide prevalence of NIDDM was estimated for 1995 and 1997, and well as projections for 2000 and 2010. Prevalence rates used for projections were chosen to reflect changes in lifestyle with economic development. The global prevalence of IDDM was estimated using published incidence rates and population figures, incorporating the likely survival time from development of IDDM. Data on diabetes complications are also summarised but no attempt has been made to extrapolate to a global estimated. In 1997, an estimated 124 million people worldwide have diabetes, 97% of these having NIDDM. By the year 2010 the total number of people with diabetes is projected to reach 221 million. The regions with the greatest potential increases are Asia and Africa, where diabetes rates could rise to 2 or 3 times those experienced today. With improvements in the treatment of IDDM, the prevalence of this form of diabetes is likely to increase as more people survive for longer after diagnosis. Increases in complications will undoubtedly follow increasing prevalence of diabetes, but population-based studies using standardised methods of diagnosis are required before reliable estimates of the extent of the problem can be made. It is hoped that the information provided in this report, and others like it, will act as an incentive to initiate or improve local diabetes monitoring and prevention strategies.