Background: Telomere length is influenced by a variety of endogenous and exogenous factors, including environmental chemicals, inflammation, and oxidative stress, and is therefore considered a marker of cumulative cellular aging or biologic age. Longer telomere length has been associated with higher levels of circulating reproductive hormones, greater parity, and reduced risk of polycystic ovary syndrome, suggesting a role of telomere length in human reproduction. However, the relationship between telomere length, as a marker of biologic age, and fecundability and fertility is unknown. Methods: We evaluated associations of preconception leukocyte telomere length with fecundability, live birth, and pregnancy loss among 1,228 participants of the EAGeR trial, which included women aged 18-40 years who were attempting to conceive. Preconception leukocyte telomere length was measured at baseline using polymerase chain reaction and reported as a ratio (T/S) in relation to population-specific standard reference DNA. The T/S ratio for each participant was then converted to base-pairs using the following formula: Base-pairs = 3274 + 2413(T/S ratio). We estimated associations of telomere length with fecundability, live birth, and pregnancy loss using Cox proportional hazards models and log-binomial models adjusted for age, body mass index, smoking, and other factors. Results: In both unadjusted and adjusted models, preconception telomere length was not associated with fecundability (adjusted fecundability odds ratio (FOR) per 1,000 base-pairs = 1.03; 95% CI = 0.85, 1.26), live birth (adjusted relative risk (RR) per 1,000 base-pairs = 1.13; 95% CI = 0.80, 1.60), or pregnancy loss (adjusted RR per 1,000 base-pairs = 1.14; 95% CI = 0.81, 1.60). Conclusions: These findings suggest that leukocyte telomere length, as a marker of biologic age, is not importantly related to fecundability or fertility among healthy reproductive-age women.