Abstract: Background Most research on children's social problem-solving skills is based on responses to hypothetical vignettes. Just how these responses relate to actual behaviour in real-life social situations is, however, unclear, particularly for children with mild intellectual disabilities (MID). Method: In the present study, the spontaneous and selected responses of 56 children with MID to hypothetical situations from the Social Problem-Solving Test for children with MID (SPT-MID) were compared to their actual behaviour in comparable staged standardized real-life conflict situations. Correlations to externalizing behaviour problems were assessed using the Teacher's Report Form (TRF). Results: The results show children with MID and accompanying externalizing behaviour problems to behave more aggressively in the staged real-life conflicts and provide more spontaneous aggressive responses to the hypothetical vignettes than children with MID and no accompanying externalizing behaviour problems; they did not, however, select more aggressive responses from the hypothetical options provided. A moderate correlation was found between the aggressiveness of the spontaneous responses in the hypothetical situations and actual behaviour in the staged real-life situations. In addition, both the spontaneous aggressive responses under hypothetical circumstances and the actual aggressive behaviour under staged real-life circumstances were related to teacher-rated aggressive behaviour in the classroom. Conclusions: It is concluded that the hypothetical vignettes from the SPT-MID do provide information on both the actual behaviour and knowledge of social problem-solving skills of children with MID.