Similarity of friends and the degree to which friendship selection criteria and similarity change as a function of age were investigated in this study. Subjects were 27 preschoolers, 34 third graders, and 30 sixth graders. Fifty-three percent were male, 47 percent were female, and 29 percent were black. Friendship choices were measured by sociometric techniques, and dyads were classified as either reciprocal or nonreciprocal. Data were obtained on intelligence, self-concept, popularity, attractiveness, birth order, number of siblings, and social class. Reciprocal dyads were found to be more similar in total and personal self-concepts, popularity, and attractiveness than were nonreciprocal pairs. Grade effects were found for popularity, attractiveness, personal self-concept, and gender. Results were discussed in terms of the cognitive-developmental approach and friendship theories. (Author/RH)