Self-reports and observations of the naturally occurring behavior of adolescents were made to investigate friendship patterns. The study was conducted during a week-long summer camp for children of university alumni attending classes. A total of 20 female and 10 male youths, ranging in age from 12 to 18 years, participated. Self-report data concerning friends, friendship, and/or demographic characteristics were gathered via brief questionnaires at the beginning and end of the day camp experience. Observational data were gathered by two observers, who recorded the intragroup friendship interactions of the 10 subjects 14 to 15 years of age. Observations were made primarily during free time in a dormitory lounge supplied with recreational and cooking equipment. Confirming earlier findings, self-report data indicated that adolescents preferred as friends those of a similar age and sex. While friendships were generally mutual, nearly half of all friendships shifted, and discordant friendships became more prevalent. The number of friends increased greatly during the week. Observational data agreed with the self-report data: individuals interacted most frequently with those they nominated as their best friends. Boys were more likely than girls to distinguish best friends from other group members by interacting with same-sex peers at close range in a physical manner. (RH)