Obesity and weight gain in adulthood are associated with an increased risk of several cancers. Telomeres play a critical role in maintaining genomic integrity, and may be involved in carcinogenesis. Using data from 647 women aged 35–74 in the U.S. and Puerto Rico (2003-4), we examined the association between current and past anthropometric characteristics and telomere length in blood cells. In a multivariate linear regression model, higher current body mass index (BMI) and hip circumference were inversely associated with telomere length. Higher BMI in the 30s was associated with shorter telomere length among women aged 40 years or older (p for trend < 0.01). Weight gain since age 30s (p for trend = 0.07) and weight cycling (p for trend = 0.04) were also inversely associated with telomere length. When current BMI and BMI at ages 30–39 were considered together, the most marked decrease in telomere length was found for women who had overweight or obese BMI at both time points (mean T/S ratio=1.26, 95% CI: 1.21–1.30) compared with women who had normal BMI at both times (mean T/S ratio = 1.33, 95% CI: 1.30–1.36). These findings support the hypothesis that obesity may accelerate aging, and highlight the importance of maintaining a desirable weight in adulthood.