CONTEXT: The impact of gender-affirming hormone therapy (HT) on cardiometabolic parameters is largely unknown. OBJECTIVE: The effects of 1 year of treatment with oral or transdermal administration of estrogen (plus cyproterone) and transdermal or IM application of testosterone on serum lipid levels and blood pressure (BP) were assessed in transgender persons. DESIGN AND METHODS: In this prospective, observational substudy of the European Network for the Investigation of Gender Incongruence, measurements were performed before and after 12 months of HT in 242 transwomen and 188 transmen from 2010 to 2017. RESULTS: Mean values are reported. In transmen, HT increased diastolic BP (2.5%; 95% CI, 0.6 to 4.4) and levels of total cholesterol (TC; 4.1%; 95% CI, 1.5 to 6.6), low-density lipoprotein-cholesterol (LDL-C; 13.0%; 95% CI, 9.2 to 16.8), and triglycerides (36.9%; 95% CI, 29.8 to 44.1); high-density lipoprotein-cholesterol levels decreased (HDL-C; 10.8%; 95% CI, -14.0 to -7.6). In transwomen, HT slightly decreased BP (systolic BP, -2.6%, 95% CI, -4.2 to -1.0; diastolic BP, -2.2%, 95% CI, -4.0 to -0.4) and decreased levels of TC (-9.7%; 95% CI, -11.3 to -8.1), LDL-C (-6.0%; 95% CI, -8.6 to 3.6), HDL-C (-9.3%; 95% CI, -11.4 to -7.3), and triglycerides (-10.2%; 95% CI, -14.5 to -5.9). CONCLUSION: Unfavorable changes in lipid profile were observed in transmen; a favorable effect was noted in transwomen. HT effects on BP were negligible. Long-term studies are warranted to assess whether and to what extent HT in trans individuals results in a differential effect on cardiovascular disease outcomes.