The purpose of this study was to investigate the effects of good and poor control of NIDDM on teeth and periodental conditions. Thirty-four NIDDM patients who underwent dental examination in 1982 were followed up for ten years. These patients (males, 19; females, 15; age, 50-69yr. in 1992) were divided into a good control group (group A, HbA1c< 8.0, n=14) and a poor control group (group B HbA1c≤8.0, n=20) according to the mean HbA1c for ten years. The duration of diabetes in group B was significantly longer than in group A. Many more decayed teeth and missing teeth were observed in group B than in group A at examinations in both 1982 and 1992. The number of missing teeth increased significnantly in both groups during ten years and the mean number of teeth lost in group B (3.9) was greater than in group A (1.6). Gingivitis and alveolar bone resorption in group B were also severer than in group A at both examinations. During ten years, gingivitis improved equally in two groups. However, alveolar bone resorption and periodontal pockets increased equally in the two groups. We conclude that diabetes should be controlled properly in order to maintain good dental conditions, and dental examination should be performed at the onset of NIDDM and periodically thereafter, because the dental condition seems to be related to the control and duration of NIDDM.