The present thesis investigated several components important to the understanding of mentalization for children who use augmentative and alternative communication (AAC). The result of the thesis demonstrated that non-verbal mental age correlated significantly with mentalization tasks, and that the participants did not significantly differ compared to a nonverbal age-matched group of children without disabilities. Different expression of active participation, which is necessary to be able to display mentalization in dialogue, was observed in analysed interaction. The children’s social networks were limited and consisted of very few peers, thus limiting the possibilities of active participation. The number of peers in the children’s social networks correlated significantly with aspects of the children’s mentalization ability. Children who use AAC display their mentalization abilities independently in social interaction and through e-mail messages to peers. A wider construct that will have relevance to mentalization in ordinary situations is described encompassing several different abilities. The development of these abilities is dependent on the child’s capacity for adapting a cognitive flexibility when reflecting and theorizing on what is happening in a given situation. The development of mentalization is also dependent on a child’s close friendships, active participation in interaction, functional language ability, and varied social networks consisting of both peers and adults.