This case report describes a young boy with concomitant genetically-confirmed Duchenne muscular dystrophy and facioscapulohumeral muscular dystrophy with a novel dystrophin mutation in exon 6 and a D4Z4 fragment of 31 kb. This child presented with a more severe phenotype than expected for either individual disease process and underscores the role for thorough diagnostic investigation in identifying atypical clinical presentations.