Oral contraceptives (OC) modulate the risk for developing cardiovascular (CV) diseases. The aim of this study was to determine whether the use of third-generation OC has an impact on markers of CV disease in genetically identical women. We performed an intrapair comparison in 27 monozygotic twin pairs, one of whom was taking third-generation OC, whereas the other was not using OC. Biometric parameters were ascertained and conventional and 24-h ambulatory blood pressure (BP) was recorded. A fasting blood sample was taken for the measurement of glucose, insulin, proinsulin, lipids, and insulin-like growth factor binding protein-1 (IGFBP-1). Insulin resistance and beta-cell function were calculated by homeostasis model assessment (HOMA). A 24-h urine sample for cortisol was obtained. Third-generation OC use increased 24-h ambulatory systolic and diastolic BP by 5.2 and 3.9 mmHg, respectively (both P=0.0003). There was no effect on glucose, insulin and proinsulin levels, and on HOMA parameters, but the IGFBP-1 levels were markedly raised (P=0.0009). The lipid profile showed a 34% increase in triglyceride levels (P < 0.0001), but also a 7% increase in HDL-cholesterol levels (P=0.037). Use of third-generation OC impacts on CV disease markers in young-adult genetically identical women. Some changes are beneficial (increased HDL-cholesterol), whereas others may be deleterious (increased BP and triglyceride levels) or have unknown effects at this time (increased IGFBP-1 levels).