This study examined the reliability of the block walk method (BWM) for observing physical activity on suburban sidewalks/streets. Trained observers simultaneously walked 40 sidewalk/street segments each 1525 m in length at a pace of 30.5 m/min while recording the number of individuals walking/bicycling/jogging and the address where the activity occurred. An activity was observed at 2.9% of the 1020 addresses walked passed. In all 41 individuals were seen walking, 4 jogging, and 3 bicycling during 400 observation minutes. Agreements were 80%, 90%, and 86.7% for address, activity type, and number of individuals. The BWM is reliable for assessing activity on suburban sidewalks/streets.