This study examined the effectiveness of an 8-week psychoeducational group program for siblings of children with autism spectrum disorder (ASD). The sample consisted of 38 siblings aged 6-15 years (M = 10.75), allocated to the experimental (n = 22) or control group (n = 16). Self-report questionnaires were administered before and after the intervention. Results indicated a significant increase in knowledge of ASD in the experimental group, but not in the control group. In addition, a statistically significant reduction in adjustment difficulties and emotional/behavioral problems in the experimental group was detected. The theoretical and practical relevance of the findings for facilitating sibling support groups is discussed.