Introduction: Social knowledge is an important aspect of social cognition that pertains to broader knowledge of social concepts and norms. People with intellectual disabilities are more likely to experience mental health challenges, and it's important to pay special attention to how comorbid conditions can affect their social cognition skills, potentially weakening these skills. Consequently, the present study seeks to compare social knowledge between two groups of adults in Bosnia and Herzegovina: those with intellectual disabilities and those diagnosed with a dual diagnosis encompassing intellectual disability and psychiatric conditions. An additional goal was to identify the factors contributing to social knowledge in these groups. Methods: The study sample included 62 adults with mild intellectual disability, divided into two groups based on their comorbid psychiatric condition. We used a demographic questionnaire, Raven's Progressive Matrices, Peabody Picture Vocabulary Test (PPVT), MINI PAS -- ADD scale, and The Social Knowledge Test to assess social knowledge and intellectual functioning. We compared the social knowledge scores between the two groups and identified the predictors of social knowledge in each group. Results: The results indicated that adult participants with dual diagnoses had lower social knowledge scores than those with intellectual disabilities only, even after controlling for intellectual functioning and verbal abilities. The predictors of social knowledge differed between the two groups, with age being the only statistically significant predictor in both groups. In individuals with intellectual disabilities, age and the presence of obsessive-compulsive disorder symptoms were important predictors of social knowledge, while in the group of participants with dual diagnoses, age and PPVT were significant predictors of social knowledge. Conclusion: This study highlights the importance of social knowledge in individuals with intellectual disabilities and dual diagnoses. The findings suggest that individuals with dual diagnoses may have a specific deficit in social knowledge that is not fully explained by their intellectual functioning or verbal abilities. Clinicians and educators should focus on identifying and addressing social knowledge deficits in individuals with dual diagnoses to improve their overall social functioning.