PURPOSE: The primary study aim was to evaluate associations of estimated weekly minutes of moderate-to-vigorous-intensity exercise from self-reports of the telephone-administered 7-Day Physical Activity Recall (7-Day PAR) with data captured by the RT3 triaxial accelerometer. METHODS: This investigation was undertaken as part of the FRESH START study, a randomized clinical trial that tested an iteratively tailored diet and exercise mailed print intervention among newly diagnosed breast and prostate cancer survivors. A convenience sample of 139 medically eligible subjects living within a 60-mile radius of the study center provided both 7-Day PAR and accelerometer data at enrollment. Ultimately, substudy subjects (n = 115) were found eligible for the FRESH START study and randomized to one of two study treatment arms. Follow-up assessments at year 1 (n = 103) and year 2 (n = 99) provided both the 7-Day PAR and the accelerometer data. RESULTS: There was moderate agreement between the 7-Day PAR and the accelerometer with longitudinal serial correlation coefficients of 0.54 (baseline), 0.24 (year 1), and 0.53 (year 2), all P values <0.01, although the accelerometer estimates for weekly time in moderate-to-vigorous physical activity (PA) were much higher than those of the 7-Day PAR at all time points. The two methods were poorly correlated in assessing sensitivity to change from baseline to year 1 (ρ = 0.11, P = 0.30). Using mixed models repeated-measures analysis, both methods exhibited similar nonsignificant treatment arm × time interaction P values (7-Day PAR = 0.22, accelerometer = 0.23). CONCLUSIONS: The correlations for three serial time points were in agreement with findings of other studies that compared self-reported time in exercise with PA captured by accelerometry. However, these methods capture somewhat different dimensions of PA and provide differing estimates of change over time.