Fragile X syndrome (FXS), a leading cause of inherited intellectual disability, most commonly results from an expansion of the CGG trinucleotide repeat in the fragile X mental retardation 1 (FMR1) gene to more than 200 copies (full mutation). The FXS phenotype differs by sex and is associated with intellectual and cognitive impairment, characteristic physical features, epilepsy, and/or behavioral challenges including autism spectrum disorder. In this patient population, tumors involving blood cells, digestive organs, the central nervous system, and testes have been described, but melanocytic tumors have not been reported. Here, we describe two maternal cousins with FXS, one of whom has melanoma and the other has atypical nevus syndrome. We discuss possible mechanisms leading to this unusual or possibly coincidental association and the difficulties in the optimal treatment of FXS patients.