Hypertension is often accompanied by type 2 diabetes mellitus. Recently, the American Diabetes Association (ADA) published guidelines on the treatment of hypertension in adult patients with diabetes mellitus. However, the views of general physicians on how to control blood pressure (BP) in diabetic patients and the impact of the ADA guidelines in Japan are still not known. We conducted an internet survey in May 2002: Questionnaires were e-mailed to a total of 3,616 medical doctors, of whom 441 (12.2%) properly responded. About half of the respondents (48.3%) had already read the ADA guidelines. Before being given an outline of the guidelines, the respondents' average BP level for starting medication was 152/94 mmHg, and the BP goal 133/83 mmHg; after reading the outline, these values were 149/92 and 132/82 mmHg, respectively. The goal BP decreased more after reading the guidelines in doctors who had not previously read the ADA guidelines than in those who had already read. After being given an outline of the ADA guidelines, 40.3% of respondents reported that they would select, as a first-line agent, an angiotensin II receptor antagonist (ARB), 35.6% an angiotensin-converting enzyme inhibitor (ACEI), and 18.6% a calcium channel blocker (CCB); as a second-line medication, 39.7% of the respondents would select a CCB. Seventy percent of doctors reported having at least one patient receiving CCB monotherapy; after reading the guidelines, 41.5% of these doctors said they would continue CCB monotherapy, 36.6% said they would add an ACEI or ARB, and 29.7% planned to change to an ACEI or ARB. In conclusion, our data suggest the impact of the ADA guidelines on the target BP and the first choice of antihypertensive medication in diabetic patients. ARBs and ACEIs became first-line medications, and CCBs became second-line medications to achieve the BP goal and prevent organ damage.