Background: Adequate knowledge on environmental correlates of physical activity (PA) in older adults is needed to develop effective health promotion initiatives. However, research in this age group is scarce and most existing studies were conducted in North America. The present study aimed to examine relationships between GIS-based neighborhood walkability and objective and self-reported PA in community-dwelling Belgian older adults. Furthermore, moderating effects of neighborhood income levels were investigated. Methods: The Belgian Environmental Physical Activity Study (BEPAS) for Seniors is a cross-sectional study in older adults (>= 65 yrs) and was conducted between October 2010 and September 2012. Data from 438 older adults living in 20 neighborhoods across Ghent (Belgium) were analyzed. Stratification of selected neighborhoods was based upon objective walkability and neighborhood income. Participants wore an accelerometer during seven consecutive days to obtain objective levels of moderate-to-vigorous physical activity (MVPA). Self-reported levels of transportation walking/cycling and recreational walking/cycling were assessed using the International Physical Activity Questionnaire (long, last 7 days version) adapted for the elderly. Multi-level regression analyses were conducted. Results: Findings showed a positive relationship between neighborhood walkability and weekly minutes of older adults' self-reported walking for transportation (B = 4.63 +/- 1.05; p < 0.001) and a negative relationship between walkability and accelerometer-derived low-light PA (B = -1.38 +/- 0.62; p = 0.025). Walkability was not related to any measure of recreational PA. A walkability x income interaction was found for accelerometer-derived MVPA (B = -1.826 +/- 1.03; p = 0.075), showing only a positive association between walkability and MVPA in low-income neighborhood residents. Conclusions: This was the first European study to examine walkability-PA relationships in older adults. These Belgian findings suggest that a high ...