To examine the prevalence and correlates of orthostatic hypotension (OH) in middle-aged adults enrolled in the Korean Health and Genome Study. Participants were 8908 individuals aged 40-69 years. Supine blood pressure (BP) was measured three times at 30-s intervals after at least 5 min of rest in the supine position and single standing BP was measured at 0 and 2 min after standing, respectively. OH was defined as a reduction in systolic BP or diastolic BP > or = 20 and 10 mmHg, respectively. The prevalence of OH at 0 and 2 min after standing was 12.3 and 2.9%, respectively. At 0 min of standing, OH frequency increased significantly with age from 6.4% in those aged 40-44 years to 23.1% in those aged 65-69 (P < 0.001). After adjustment for age and other characteristics, hypertension was associated with a 1.7-fold excess in the odds of OH in men and a 1.6-fold excess in women (P < 0.001). In contrast, an increase in body mass index (BMI) on the order of 5 kg/m2 was associated with a 20-30% reduction in the odds of OH (P < 0.001). Diabetes in women was also associated with a 1.4-fold excess in the odds of OH (P < 0.05). An increase in triglyceride by 136 mg/dl in men was associated with an increase in the odds of OH (P < 0.05). In conclusion, the prevalence and correlates of OH other than diabetes and triglycerides were notably similar in men and women. While the association between hypertension and OH has been observed elsewhere, low BMI in Korean adults with OH may be an important marker for subclinical morbidity or coexisting risk factors that need to be identified.