In this study multiple deletions of mitochondrial genome were found in a patient presenting with periodic attacks of paralysis. Morphological studies revealed mitochondrial abnormalities along with typical histopathological features of periodic paralysis. Southern blot and PCR analysis revealed multiple mtDNA deletions. Our patient could be affected by two unrelated diseases, idiopathic periodic paralysis and presymptomatic mitochondrial myopathy. Alternatively, mtDNA alterations and oxidative deficiency might express themselves phenotypically as periodic paralytic attacks, although this correlation has never been reported.