Social skills are critical for academic, social, and psychological success of children with both typical and atypical development. Boys with fragile X syndrome (FXS) are at high risk for social skill impairments, given intellectual impairments and secondary conditions. The present study examines the impact of adaptive behavior, autism symptoms, and anxiety symptoms to social skills at the composite and subdomain level in boys with FXS across age. This cross-sectional study included boys with FXS (3–14 years) contrasted to age-matched typical control boys. Results revealed that social skills are generally within developmental expectations, with adaptive behavior as the primary predictor. Anxiety and autism symptoms emerged as additive risk factors, particularly in the areas of responsibility and self-control.