The study aimed to establish criteria for diagnosing 'obesity disease' in Japan, considering obesity-related complications. A total of 1,193 Japanese subjects (775 men, 418 women) were examined, including those undergoing health checks and those visiting obesity clinics. Visceral fat area (VFA) and subcutaneous fat area (SFA) were measured using CT scans, along with anthropometric parameters such as BMI, waist circumference (W), and waist-to-hip ratio. Obesity-related complications included hyperglycemia, dyslipidemia, and hypertension. The number of complications increased with BMI, reaching an average of more than 1.0 at a BMI of 25. BMI showed a strong correlation with SFA but a weaker correlation with VFA. VFA was found to be a better predictor of obesity-related complications, with a threshold of 100 cm² being optimal. Waist circumference (W) was closely related to VFA, with W values of 84.4 cm in men and 92.5 cm in women corresponding to 100 cm² of VFA. The study concluded that BMI ≥25 is appropriate for defining obesity in Japan, with VFA ≥100 cm² as a key indicator for obesity-related disorders. The new criteria for 'obesity disease' include defining obesity as BMI ≥25, identifying high-risk obesity through CT scans, and using waist circumference and VFA for diagnosis. The study emphasizes the importance of visceral fat in obesity-related complications and proposes that a BMI of 25 and a VFA of 100 cm² are suitable thresholds for diagnosing obesity disease in Japan. The study also highlights the need for practical screening methods and the importance of considering visceral fat in the diagnosis of obesity-related disorders.The study aimed to establish criteria for diagnosing 'obesity disease' in Japan, considering obesity-related complications. A total of 1,193 Japanese subjects (775 men, 418 women) were examined, including those undergoing health checks and those visiting obesity clinics. Visceral fat area (VFA) and subcutaneous fat area (SFA) were measured using CT scans, along with anthropometric parameters such as BMI, waist circumference (W), and waist-to-hip ratio. Obesity-related complications included hyperglycemia, dyslipidemia, and hypertension. The number of complications increased with BMI, reaching an average of more than 1.0 at a BMI of 25. BMI showed a strong correlation with SFA but a weaker correlation with VFA. VFA was found to be a better predictor of obesity-related complications, with a threshold of 100 cm² being optimal. Waist circumference (W) was closely related to VFA, with W values of 84.4 cm in men and 92.5 cm in women corresponding to 100 cm² of VFA. The study concluded that BMI ≥25 is appropriate for defining obesity in Japan, with VFA ≥100 cm² as a key indicator for obesity-related disorders. The new criteria for 'obesity disease' include defining obesity as BMI ≥25, identifying high-risk obesity through CT scans, and using waist circumference and VFA for diagnosis. The study emphasizes the importance of visceral fat in obesity-related complications and proposes that a BMI of 25 and a VFA of 100 cm² are suitable thresholds for diagnosing obesity disease in Japan. The study also highlights the need for practical screening methods and the importance of considering visceral fat in the diagnosis of obesity-related disorders.