A sample of 301 Philadelphia adolescents were assessed for substance use and place-based social network quality, a weighted variable based upon risky and protective behaviors of alters. The network measure was anchored in routine locations identified as safe, risky, important, or favorite. Results show young females' (13-16) substance use was strongly associated with their place-based social networks compared to older females (17-20) and compared to young and older males. Younger females' protective networks reduced their likelihood of substance use compared to females with risky networks (OR = 0.94, CI = 0.89-0.99, p less than 0.05), while young males experienced no protective network effects. Older females' protective networks reduced the likelihood of substance use compared to those with risky networks (OR = 0.96, CI = 0.93-0.99, p less than 0.005). Older males' protective networks also reduced their likelihood of substance use (OR = 0.86, CI = 0.74-0.99, p less than 0.05). Results highlight the varying affects of place, gender, and age on adolescent social network protection and associated risk for substance use. (Contains 5 tables.)