Background: Mutations of mitochondrial DNA (mtDNA) cause a broad spectrum of clinical phenotypes. Anecdotal evidence suggests that voice and swallow problems are a common feature of these diseases. Aims: To characterize accurately the prevalence and severity of voice and swallow problems in a large cohort of patients with mitochondrial disease. Methods & Procedures: Patients with proven mitochondrial disease were sent validated questionnaires to assess both voice and swallow function. The presence of voice and swallow symptoms was correlated with other clinical features of mitochondrial disease in affected patients. Outcomes & Results: From the original 177 patients contacted, 98 swallowing status questionnaires and 96 Voice Handicap Index questionnaires were returned, response rates of 55% and 54%, respectively. Swallow: 48% of patients reported more difficulties with swallowing than control participants. Patients with single mtDNA deletions were most likely to report problems (65.2%), with patients with an m.8344A greater than G point mutation least likely (33.3%). All genotypes had a mean severity score in excess of the normal range, the highest mean score being found in the single large-scale mtDNA deletion group (10.12), the lowest in the m.3243A greater than G group (5.56) Voice; 48% of patients reported some difficulty with voice. Patients with single large-scale deletions showed the highest prevalence (65.2%), patients with the m.3243A greater than G mutation the lowest (33%). The most severe voice difficulties were reported by patients with an m.8344A greater than G point mutation. Patients with an m.3243A greater than G point mutation had the mildest and lowest incidence of voice problems. All genotypes scored outside of the normal range expected on the VHI overall ([greater than or equal]11.5 in control trials). Patients with an m.8344A greater than G point mutation reported a significantly higher degree of physical voice handicap than m.3243A greater than G patients (13.13 versus 4.40, p = 0.02). In patients with either single or multiple mtDNA deletions the likely pathophysiological mechanism is of proximal muscle weakness, whereas in patients with the m.8344A greater than G mutation cerebellar ataxia is the likely cause. Conclusions & Implications: Dysphagia and dysarthria have been identified as symptoms in previous research, however the prevalence and pathophysiology of these symptoms have not been explored. This paper indicates that voice and swallow problems are a common, though predominantly mild feature of mitochondrial disease and that there is a core group of pathophysiological symptoms linked to the presence of voice and swallowing problems. This paper recommends early referral to speech and language therapists to identify emerging dysphonia and dysphagia and to provide appropriate intervention. (Contains 3 tables.)