The incidence and mortality of acute myocardial infarction (AMI) remain low in Japan despite major dietary changes and worsening cardiovascular risk factors, a situation that should have resulted in a substantial increase in AMI rates (Japanese paradox). The current trend in the incidence of AMI was examined for the period 1990-2001 by use of data from the Takashima AMI Registry covering a stable population of approximately 55,000 in central Japan. AMI incidence rates (per 100,000 person-years) and 95% confidence intervals were calculated for 1990-1992, 1993-1995, 1996-1998, and 1999-2001. The incidence trend was determined by calculating the average annual change in percentage across the years. There were 352 (men: n = 224; women: n = 128) registered first-ever AMI cases during 1990-2001. The age-adjusted incidence rate of all AMI showed a gradual increase from 39.9 (95% confidence interval (CI): 29.8, 50.0) in 1990-1992 to 62.6 (95% CI: 51.5, 73.7) in 1999-2001. In men, the age-adjusted incidence rate increased from 66.5 (95% CI: 46.4, 86.6) in 1990-1992 to 100.7 (95% CI: 78.6, 122.7) in 1999-2001. In women, fluctuation was observed after an initial steep increase. The average annual incidence increased by 7.6% (95% CI: 3.5, 11.7) among men and by 8.3% (95% CI: 1.02, 15.6) among women. To the best of the authors' knowledge, this is the first study to report an increasing trend of AMI in a Japanese population.