We report the case of a 38-year-old woman, affected by a cutaneous form of mycosis fungoides (MF) who presented with a history of loud snoring associated with sleep apnea. A polysomnographic study confirmed the presence of severe obstructive sleep apnea syndrome (OSAS). Cranial and neck MRI revealed a neoplastic infiltration of the tongue base and the posterior pharynx wall. Upper airway neoplastic infiltration is rarely reported as a cause of OSAS and extra-cutaneous localizations of MF are uncommon. This is the first case in the literature of a patient with nocturnal polysomnogram documented OSAS caused by a mucosal involvement of MF.