The study found that links between social-network measures and substance use varied by type of substance and social context. A link was found between the characteristics of social networks and gender and the socioeconomic status (SES) of most of the students' parents in a school. Girls and students from higher SES schools were more likely to socialize in groups, be more "popular" (have more students list them as friends), and be more "expansive" (list more students as friends). Smoking was lower than average among students who socialized in groups and was higher than average for students who socialized in pairs or listed no friends. Smoking was positively related to popularity only in higher SES schools, where smoking rates were significantly lower. This may represent a popular counterculture associated with smoking in such schools. The use of drugs and alcohol were highest among the most popular students, and alcohol use was the highest among students who listed the most number of friends ("expansive"). Data were obtained from the Teenage Health in Schools study (Gordon and Turner, 2003; Turner et al., 2006). The nine participating schools are located in and around Glasgow, Scotland. The study involved 13 and 15 year-olds (n=3,146) in a school-based survey. The questionnaire focused on three social network measures: sociometric position (activities most often in groups, pairs, or alone); popularity (friendship nominations received); and expansiveness (friendship nominations made). The study examined the pattern of these social network measures by age, gender, and school SES, as well as their relationships with substance use (current smoking, experience with drugs, and alcohol use in the previous week). 4 tables, 1 figure, and 36 references