Objectives: How to contain medical expenditures is a universal problem. The Japanese government has increased patient co-payments to control it. The purpose of this study is to clarify whether the increase in co-payments to 30 percent prevented patients with hypertension or diabetes mellitus from receiving necessary care in the Employee Health Insurance System.

Methods: The subjects were 211 patients with hypertension and 66 patients with diabetes mellitus who regularly visited physicians from October 2001 to March 2002 and were defined as a cohort that needed health care, and their medical indicators were examined between April and September 2002 (prestage) and between April and September 2003 (poststage).

Results: In the hypertensive patients with no complications, the compliance rate was 89.9 percent and 88.0 percent in the prestage, and poststage, respectively, showing no significant change. In the hypertensive patients with complications, the compliance rate was 90.5 percent and 92.1 percent in the prestage and poststage, respectively, showing no significant change. In the diabetic patients with complications, the compliance rate was 77.5 percent and 79.2 percent, in the prestage and poststage, respectively, with no significant change. In the diabetic patients with no complications, however, the compliance rate was 83.7 percent and 66.7 percent, in the prestage and poststage, respectively. A significant decrease was observed among diabetic patients without complications.

Conclusions: Increasing co-payments reduced necessary preventive care in diabetic patients without complications.