The present study examined trajectories of adaptive behavior, behavior problems, psychological symptoms, and autism symptoms in adolescents and adults with fragile X syndrome (n = 147) over a three-year period. Adaptive behavior significantly increased over time, particularly for adolescents, and the severity of behavior problems decreased over time. Family environmental factors predicted phenotypic variables net of gender, intellectual disability status, and medication use. Maternal warmth was associated with higher levels of adaptive behavior, lower levels of autism symptoms, and decreases in behavior problems over time. Maternal depressive symptoms and criticism were associated with higher levels of psychological symptoms. Implications for interventions are discussed.