To examine the distribution and cardiovascular risk correlates of serum triglycerides, a cross-sectional population study based on annual health examinations at the workplace was performed in 2199 young Japanese adults aged 23 to 37 years. Triglyceride levels showed significant sex (male > female) differences, and the percentages of those with high triglycerides (≥ 150 mg/dl) were 9.4% for males and 0.8% for females. In terms of conjoint trait of dyslipidemia, 86.1% of males displayed normal levels of both triglycerides (< 150 mg/dl) and high-density lipoprotein (HDL) cholesterol (≥ 40 mg/dl), while 98.7% of females had normal values. Age-and sex-specific triglyceride levels above the 75th percentile (equivalent to 82-116 mg/dl for males and 56-63 mg/dl for females) increased the risk (odds ratio (OR)) for having obesity, hypertension, and hyperuricemia by 2.9 (95% confidence interval (CI)=2.0-4.3), 1.7 (CI=1.1-2.9), and 3.0 (CI=1.6-5.9), respectively. The respective ORs for triglyceride levels above the 75th percentile and HDL cholesterol below the 25th percentile (equivalent to 45-49 mg/dl for males and 58-63 mg/dl for females), compared with triglyceride levels the 75th percentile or less and HDL cholesterol levels the 25th percentile or more, were 8.7 (CI=5.8-12.9), 2.2 (CI=1.5-3.3), and 6.0 (CI=3.2-11.5). Our results suggest a threshold effect of triglyceride levels considered as normal on enhanced cardiovascular risk in young Japanese adults, especially in those with low HDL cholesterol levels.