['To determine whether there are common symptoms within different phenotypes of the mitochondrial DNA A3243G mutation.', 'A series of 52 adults with mitochondrial encephalomyopathies and their symptomatic relatives were screened for the A3243G mutation using restriction enzyme analysis. In addition to clinical examination, patients with the mutation underwent audiometry.', 'The A3243G mutation was identified in 16 patients (10 index patients and 6 symptomatic relatives). Six of these patients presented with strokelike episodes and met the classical criteria of MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes), and one had MELAS/MERRF (myoclonic epilepsy with ragged-red fibers) overlap syndrome. Two patients presented with strokelike episodes but did not meet the classical criteria of MELAS. Predominant features of the 8 other patients were myopathy with hearing loss and diabetes mellitus (n = 1), chronic progressive external ophthalmoplegia (n = 1), diabetes mellitus with hearing loss (n = 1), painful muscle stiffness with hearing loss (n = 1), cardiomyopathy (n = 1), diabetes mellitus (n = 1), and hearing loss (n = 2). In 11 of 16 patients, hearing impairment was obvious on clinical examination. Furthermore, all 5 patients with normal hearing on clinical examination showed subclinical hearing loss; in 4, hearing loss was more pronounced than age-related hearing impairment and in 1, hearing loss can be age related as well.'] Is hearing impairment common in various phenotypes of the mitochondrial DNA A3243G mutation?