Achondroplasia is the most common type of short-limbed dwarfism in children resulting from fibroblast growth factor receptor (FGFR) mutations. Activating mutations of FGFR3 also result in other forms of skeletal dysplasia and craniosynostosis. Acanthosis nigricans is associated with these skeletal dysplasias and we recently encountered a skeletal dysplasia along with acanthosis nigricans in a young boy. We report the case due its unusual nature affecting one of twin brothers.