OBJECTIVES:  To classify types of neighborhood environment and to examine the gender-specific cross-sectional associations between these neighborhood types and adolescents' perceptions of physical activity–related neighborhood barriers and facilitators.  METHODS:  This cross-sectional study was conducted with a sample of 350 high school students in Baltimore, Maryland, in 2006. Participants completed the Neighborhood Environment Walkability Scale (NEWS). Objectively GIS-measured attributes of urban form came from various sources. Classification of built environment/neighborhood types was achieved by factor analysis and cluster analysis.  RESULTS:  Four neighborhood types were identified: (1) arterial development; (2) inner-city area; (3) suburban residential; and (4) central business district. Girls who lived in suburban residential areas were less likely than their central business district counterparts to perceive the protective effects of crosswalks and pedestrian traffic signals. Girls living in inner-city neighborhoods were more likely than their central business district counterparts to perceive the traffic as being slow. Boys' perceptions of their neighborhood did not vary by neighborhood pattern.  CONCLUSIONS:  Girls appear to be more sensitive to their environment and perceive more physical activity–related built environment barriers compared to boys. Efforts to overcome physical activity barriers salient for adolescent girls should be tailored to the type of neighborhood.