Objective— Familial combined hyperlipidemia (FCHL) characterized by high serum total cholesterol and/or triglycerides (TGs) is a common dyslipidemia predisposing to coronary artery disease (CAD). Recently, the upstream transcription factor 1 ( USF1 ) was linked and associated with FCHL and TGs in Finnish FCHL families. Here we examined the previously associated rs3737787 SNP in extended Dutch FCHL families (n=532) and in a cohort of US subjects who underwent diagnostic coronary angiography (n=1533). Methods and Results— In males of the Dutch FCHL families, we observed significant sex-dependent associations between the common allele of rs3737787 and FCHL, TGs, and related metabolic traits ( P =0.02 to 0.006). In the U.S. Whites, sex-dependent associations with TGs and related metabolic traits were observed for the common allele of rs3737787 in males ( P =0.04 to 0.02) and rare allele in females ( P =0.05 to 0.002). This intriguing relationship was further supported by the highly significant genotype x sex interactions observed for TGs in the Dutch and TGs and body mass index (BMI) in U.S. White subjects with CAD ( P =0.0005 to 0.00004). Conclusion— These data show that USF1 influences several cardiovascular risk factors in a sex-dependent manner in Dutch FCHL families and U.S. Whites with CAD. A significant interaction between sex and genotype was shown to affect TGs and BMI.