The analysis, based on interviews with 15 brothers and 25 sisters of 27 incarcerated youths, categorized the domains of gender-related social conditions as activity (comprised of range, timing, pace, and focus) and definition (comprised of self- definitions, peer pressures, societal definitions, physical differences, and the meanings of crime). The data showed that gender-related conditions worked together to produce more delinquency among boys and less among girls. Each dimension of activity placed the boys in potentially more vulnerable circumstances, with fewer social constraints. Each source of gender definition had the potential to reinforce male delinquency and inhibit female delinquency. The data are generally consistent with power-control theory, routine activities theory, and opportunity theory. 3 tables, 1 note, and 64 references