Mitochondrial DNA (mtDNA) deletions have been noted in small quantities in a handful of atypical cases of myotonic dystrophy and there are clinical and pathological parallels between this autosomal dominant disease and certain mitochondrial myopathies where such deletions are well recognised. We studied 20 individuals from typical pedigrees of myotonic dystrophy (of whom 19 were clinically affected) with Southern blot analysis, and 2 of the affected individuals with PCR analysis of mtDNA, but were unable to demonstrate the previously noted deletions in any quantity by either method. We conclude that especially in view of known naturally occurring large scale and minor length variants in mtDNA, these previous findings are of dubious relevance to the disease.