Background: Asian populations are at increased risk of diabetes mellitus (DM) and cardiovascular diseases (CVD). The hypertriglyceridemic waist (HTGW) phenotype, a proxy for visceral adiposity, is a recognized marker of cardiometabolic dysfunction. This study aimed to investigate the prevalence and determinants of the HTGW phenotype, as well as its association with DM and CVD in the Indonesian and Korean populations—two Asian cohorts with distinct sociodemographic and lifestyle characteristics. Methods: This cross-sectional study analyzed national health survey data from Indonesia (n = 34,256) and Korea (n = 33,536). HTGW was defined as the coexistence of abdominal obesity (waist circumference ≥ 90 cm in men; ≥80 cm in women) and elevated serum triglycerides (≥ 150 mg/dL). Multivariable logistic regression analyses assessed lifestyle determinants of HTGW phenotype and its associations with DM and CVD. Results: HTGW prevalence was comparable in Indonesia (13%) and Korea (12%), although sex-specific patterns differed: more women in Indonesia (16%) but more men in Korea (17%) exhibited the phenotype. Smoking and alcohol consumption increased the odds of HTGW phenotype [adjusted prevalence odds ratio (aPOR) (95%CI): 1.07 (0.94–1.22) and 1.46 (1.04–2.03) in Indonesians; 1.67 (1.52–1.85) and 1.31 (1.20–1.43) in Koreans, respectively], whereas physical activity lowered the odds [0.83 (0.75–0.91) in Indonesians; 0.53 (0.49–0.58) in Koreans]. Compared to individuals without the phenotype, those with HTGW had higher odds of DM [2.42 (2.13–2.74) in Indonesians; 1.96 (1.76–2.18) in Koreans] and CVD including hypertension [1.78 (1.60–1.98) in Indonesians; 1.95 (1.76–2.15) in Koreans], with stronger associations observed among women in both populations. Conclusions: HTGW prevalence was comparable in Indonesia and Korea, but sex-specific differences suggest distinct underlying mechanisms and the need for tailored interventions. Smoking and alcohol use were key contributors, whereas physical activity was protective, underscoring modifiable lifestyle factors in phenotype expression. HTGW was consistently associated with DM and CVD across both populations, reinforcing its value as a marker of cardiometabolic risk. © The Author(s) 2025.