The prevalence of diabetes has been increasing greatly, but WHO's predicted 39% rise in the global rate of diabetes from 2000 to 2030 might be an underestimate. We aimed to assess diabetes trends in Ontario, Canada. Using population-based data, including a validated diabetes database from the province of Ontario, Canada, we examined trends in diabetes prevalence and mortality from 1995 to 2005, and incidence from 1997 to 2003, in adults aged 20 years or older. Age-adjusted and sex-adjusted diabetes prevalence increased by 69%, from 5.2% in a population of 7,908,562 in 1995 to 8.8% of 9,276,945 in 2005. Prevalence increased by 27% from 6.9% in a population of 8,457,720 in 2000 to 8.8% of 9,276,945 in 2005. Although prevalence rates have remained higher in people aged 50 years or older (7.1% of 3,675,554) than in those aged 20-49 years (3.5% of 5 601 391), rates increased to a greater extent in the younger population (94%vs 63%, p<0.0001). A 31% increase occurred in yearly incidence over 6 years, from 6.6 per 1000 in 1997 to 8.2 per 1000 in 2003. The adjusted mortality rate in people with diabetes fell by 25% from 1995 to 2005. The prevalence of diabetes in Ontario, Canada increased substantially during the past 10 years, and by 2005 already exceeded the global rate that was predicted for 2030. This increase in prevalence is attributable to both rising incidence and declining mortality. Effective public-health interventions aimed at diabetes prevention are needed, as well as improved resources to manage the greater number of people living longer with the disease.