Background: This study examined how adolescents with mild intellectual disabilities define qualities of friendship and discussed the extent to which these definitions adhere to established definitions of close friendship. Materials and Methods: The study was based on qualitative interviews with 11 adolescents in secondary school. The interviews were supplemented with information from six parents. A thematic structural analysis was used to identify themes. Results: Qualities of friendship were categorized as mutual preference, mutual enjoyment, shared interactions, care, mutual trust and bonding. The criteria for close friendship seem to be fulfilled, albeit to a moderate degree. Closeness and reciprocity appear to be significant in this study, although these features have been considered less relevant within this target group in previous research. Conclusions: Differences in definitions may explain divergent results compared with other studies, and the need to achieve equivalence in friendship may be another.