Objectives : This study was performed to determine whether an increase in abdominal obesity is an independent risk factor for impaired fasting glucose and type 2 DM. Methods : Among 24,212 adults over 30 years who undertook comprehensive medical screening examinations from Jan to Dec 1999, in a university hospital in Seoul, a total of 11,183 subjects were selected who had no DM at baseline and who were followed up more than once by Dec 2002. The average follow up period was 2.4 (${pm}0.5$) years. DM was defined as having a fasting glucose level $geq$ 126mg/dl, and impaired fasting glucose as showing a fasting glucose level between 110 and 125 mg/dl. Body weight, height and waist circumference (WC) were simultaneously measured with blood sampling. The relative risks (RRs) for DM and impaired fasting glucose by WC were calculated using Cox proportional hazard model. Ageadjusted rates were estimated by direct standardization using a reference population of 2000 from 30 to 80 years. Results : The average age of the subjects was 41.7 (${pm}7.0$) years; males 41.2 (${pm}6.5$) and females 45.6 (${pm}9.2$). RRs for type 2 DM by WC with the reference group of WC < 80cm were as follows: 2.66 (95%, CI $0.55{sim}12.8$) for WC of $80{sim}89cm$ in men, 5.92 (95%, CI $1.08{sim}32.3$) for WC $geq$ 90 cm in men, and 2.64 (95%, CI $0.23{sim}29.8$) for WC of $80{sim}89cm$ in females. RRs for impaired fasting glucose by WC were 3.03 (95%, CI $2.18{sim}4.22$) for WC $80{sim}89cm$ in men, 6.10 (95%, CI $4.25{sim}8.75$) for WC $geq$ 90cm in men, and 1.56 (95%, CI $0.43{sim}5.67$) for WC $80{sim}89cm$ in women, and 8.08 (95%, CI $2.22{sim}29.4$) for WC $geq$ 90cm in females. These results remained significant after adjustment for age, BMI and fasting glucose concentrations at baseline in both sexes. Annual increment of more than 1 cm in WC was associated with the development of DM and impaired fasting glucose independently of age, sex, BMI, or presence of abdominal obesity. Conclusion : In Korean adults, abdominal obesity increased the risk for the development of type 2 diabetes and impaired fasting glucose. This result supports many other prospective studies suggesting abdominal obesity as a risk factor for type 2 diabetes.