Purpose: To estimate risks of incident type 2 diabetes (T2D) and stage 2 and greater hypertension associated with self-reported and accelerometer-determined moderate-vigorous physical activity (MVPA) separately and adjusted for each other. Methods: The sample included 2291 black and white men and women, ages 38–50 yr, in the Coronary Artery Risk Development in Young Adults (CARDIA) fitness study, conducted during the year 20 core CARDIA examination. Accelerometer-determined (Actigraph, LLC. model 7164) MVPA (MVPA-Acc), assessed at year 20, was defined as minutes per day of counts ≥2020 min-1. Self-reported MVPA (MVPA-SR) was assessed at year 20 using the CARDIA Physical Activity History. Incident T2D was ascertained at years 25 and 30 from fasting glucose, 2 h glucose tolerance test, HbA1c, or diabetes medication; incident hypertension was ascertained at those same times from measured blood pressure or use of antihypertensive medications. Modified Poisson regression models estimated relative risk (RR) of incident (years 25 and 30) T2D or hypertension, associated with middle and high tertiles of year 20 MVPA-Acc alone, year 20 MVPA-SR alone, and both, adjusted for each other, relative to bottom tertile. Results: In men, MVPA-Acc, but not MVPA-SR, was associated with a 37% to 67% decreased risk of incident T2D in a dose–response relation that persisted with adjustment for BMI, Similar associations were observed in women, although the risk reduction was similar in the second and third tertiles, relative to the bottom tertile. In both men and women, MVPA-Acc was marginally associated with reduced risk of incident stage 2 and greater hypertension, but only after adjustment for BMI, whereas MVPA-SR was not associated in either sex. Conclusions: Accelerometer-determined MVPA may provide more consistent risk estimates for incident diabetes than self-reported MVPA.