Background— Leukocyte telomere length (LTL) decreases over the adult life course owing to the cumulative burden of oxidative stress, inflammation, and exposure to vascular risk factors. Left ventricular (LV) mass is a biomarker of long-standing exposure to cardiovascular disease risk factors. We hypothesized that LTL is related inversely to LV mass. Methods and Results— We related LTL (measured by Southern blot analysis) to echocardiographic LV mass and its components (LV diastolic dimension and LV wall thickness) in 850 Framingham Heart Study participants (mean age 58 years, 58% women) using multivariable linear regression with adjustment for age, sex, height, weight, systolic blood pressure, hypertension treatment, and smoking. Overall, multivariable-adjusted LTL was positively related to LV mass (β-coefficient per SD increase 0.072; P =0.001), LV wall thickness (β=0.053; P =0.01), and LV diastolic dimension (β=0.035; P =0.09). We observed effect modification by hypertension status ( P for interaction=0.02 for LV mass); LTL was more strongly associated with LV mass and LV wall thickness in individuals with hypertension (β-coefficient per SD increment of 0.10 and 0.08, respectively; P <0.01 for both). Participants with hypertension who were in the top quartile of LV mass had LTL that was 250 base pairs longer than those in the lowest quartile ( P for trend across quartiles=0.009). Conclusions— In contrast to our expectation, in the present community-based sample, LTL was positively associated with LV mass and wall thickness, especially so in participants with hypertension. These data are consistent with the hypothesis that longer LTL may be a marker of propensity to LV hypertrophy.