Background: Telomere length is a marker of cellular aging and is linked with multiple chronic diseases, while parity has been linked to health outcomes such as breast cancer and obesity. One other inquiry has been made into how parity is associated with telomere length; another investigation could further explore how genetics and reproduction relate. Purpose: To evaluate the association between telomere length and parity among a nationally representative sample of US women. Methods: We analyzed data on 1556 women ages 20 to 44 from the National Health and Nutrition Examination Survey, 1999-2002. Parity, defined as number of previous live births, was ascertained by questionnaire. Leukocyte telomere length was measured by polymerase chain reaction (PCR) and reported as a ratio in relation to standard reference DNA. The relationship between leukocyte telomere length and parity (parous/nulliparous) was examined using survey weighted linear regression accounting for the complex survey design. Models were adjusted for race, age, body mass index, income-to-poverty ratio, education, and smoking status. Given racial differences in telomere length, interactions by race were examined. Results: Among reproductive age women in the US, the mean leukocyte telomere length in parous women was 6.4% (95% CI: 2.2, 10.4%) shorter than nulliparous women. After adjustment for confounding factors, parous women had 4.1% shorter telomeres (95% CI: 0.7%, 7.4%). No statistically significant interaction by race was observed. Conclusions: These findings in a nationally representative sample of US reproductive age women suggest that history of live birth may be associated with shorter telomeres.