Ku70/80 are genes responsible for the repairing of DNA double-strand breaks and they function as a regulatory subunit of the DNA-dependent protein kinase. Their expression has not yet been investigated in malignant melanomas of the oral cavity. These tumours are characterized by very poor prognosis and etiology independent of UV-radiation. We investigated 29 malignant melanomas of the oral cavity for the expression of Ku70/80 proteins. Ku70 expression was preserved in 21 out of 29 tumours and the percentage of Ku70-positive cells did not exceed 76%. Ku80 was found in 19 out of 29 tumours and the percentage of Ku80-positive cells peaked at 62%. Correlations between Ku70 and Ku80 expression were lost (p>0.05). We conclude that decreased Ku70/80 expression in malignant melanomas of the oral cavity and loss of correlation between these markers may influence progression of oral melanomas.