The study's aims were to examine whether residential self-selection differed according to socio-demographic characteristics and objectively assessed neighborhood walkability; and, whether objectively assessed walkability was a significant correlate of physical activity (PA) beyond residential self-selection. In total, 412 adults (aged 20-65 years) completed a socio-demographic questionnaire, the long IPAQ, a neighborhood selection questionnaire and wore an accelerometer for seven days. Walkability characteristics were an important reason for selecting the current neighborhood and were more important for women, older and less-educated adults, but not for high-walkable neighborhood residents. Both in the total sample and in participants with high residential self-selection scores, walkability was positively related to active transportation and objectively measured moderate-to-vigorous PA. Designing walkable neighborhoods may help to increase adults' PA, even in those for whom walkability is an important criterion when choosing their neighborhood. However, findings from studies with longitudinal and controlled designs are required to provide more strongly causal evidence.