Fragile X syndrome (FXS) is the most common form of inherited intellectual disability. Previous studies have implicated mGlu5 in the pathogenesis of the disease, and many agents that target the underlying pathophysiology of FXS have focused on mGluR5 modulation. In the present work, a novel pharmacological approach for FXS is investigated. NNZ-2566, a synthetic analog of a naturally occurring neurotrophic peptide derived from insulin-like growth factor-1 (IGF-1), was administered to fmr1 knockout mice correcting learning and memory deficits, abnormal hyperactivity and social interaction, normalizing aberrant dendritic spine density, overactive ERK and Akt signaling, and macroorchidism. Altogether, our results indicate a unique disease-modifying potential for NNZ-2566 in FXS. Most importantly, the present data implicate the IGF-1 molecular pathway in the pathogenesis of FXS. A clinical trial is under way to ascertain whether these findings translate into clinical effects in FXS patients.