Bariatric surgery patients report significant pre- to postoperative increases in physical activity (PA). However, it is unclear whether objective measures would corroborate these changes. The present study compared self-reported and accelerometer-based estimates of changes in moderate-to-vigorous intensity PA (MVPA) from pre- (pre-op) to 6 months postsurgery (post-op). Twenty bariatric surgery (65% laparoscopic-adjustable gastric banding, 35% gastric bypass) patients (46.2 ± 9.8 years, 88% female, pre-op BMI = 50.8 ± 9.7 kg/m(2)) wore RT3 accelerometers as an objective measure of MVPA and completed the Paffenbarger Physical Activity Questionnaire (PPAQ) as a subjective measure before and 6 months after bariatric surgery. Time (min/week) spent in MVPA was calculated for the PPAQ and RT3 (≥ 1-min and ≥ 10-min bouts) at pre-op and post-op. Self-reported MVPA increased fivefold from pre-op to post-op (44.6 ± 80.8 to 212.3 ± 212.4 min/week; P < 0.005). By contrast, the RT3 showed nonsignificant decreases in MVPA for both ≥ 1-min (186.0 ± 169.0 to 151.2 ± 118.3 min/week) and ≥ 10-min (41.3 ± 109.3 to 39.8 ± 71.3 min/week) bouts. At pre-op, the percentage of participants who accumulated ≥ 150-min/week of MVPA in bouts ≥ 10-min according to the PPAQ and RT3 was identical (10%). However, at post-op, 55% of participants reported compliance with the recommendation compared to 5% based on RT3 measurement (P = 0.002). Objectively-measured changes in MVPA from pre-op to 6 months post-op appear to be much smaller than self-reported changes. Further research involving larger samples is needed to confirm these findings and to determine whether self-report and objective PA measures are differentially associated with surgical weight loss outcomes.