Almost one-in-ﬁve infants at high familial risk for autism spectrum disorder (ASD), due to having an older sibling withan ASD diagnosis, develop ASD themselves by age 3 years. Less is known about the longer-term outcomes of high-riskinfants. To address this issue, we examined symptoms of ASD and associated developmental conditions (attention-deﬁcit/hyperactivity disorder (ADHD); anxiety), language, IQ, and adaptive behaviour at age 7 years in high- and low-risk children studied from infancy. We compared outcomes between high-risk children who met criteria for ASD at age7, high-risk children without ASD, and low-risk control children. Diagnostic stability between 3 and 7 years was moder-ate. High-risk siblings with ASD showed elevated levels of ADHD and anxiety symptoms and lower adaptive behaviourthan low-risk control children. High-risk siblings without ASD had higher repetitive behaviours, lower adaptive func-tioning, and elevated scores on one anxiety subscale (Separation Anxiety) compared to low-risk controls. The ﬁndingsindicate that the difﬁculties experienced by high-risk siblings at school age extend beyond ASD symptoms. Betterunderstanding of these difﬁculties may improve models of the development of co-occurring problems seen in childrenwith ASD.