Children's ability to establish peer relationships is an important issue in early childhood education. Making and maintaining friendships fosters children's social skills development. This longitudinal study examines the transitivity, mutuality, and stability of five- and six-year-old children's peer relationships over one preschool academic year. Participants included 16 children in a southwestern Finnish preschool. The data consist of interviews with the children (80 total) conducted at five separate time points using sociometric nomination techniques. Social network analysis methods were used to investigate the nature and change in the children's peer relationships. The study contributes to the extant literature by describing how the children's friendship ties stabilized over one year. It finds that, instead of extending their peer networks, the children sought stable and mutual relationships, exhibiting a stronger preference for gender segregation than age similarity. Daily pedagogical arrangements in the seating order had some influence on peer relationships.