Nowadays, the use of formalyn fixed tissue for forensic identification is frequently requested. This is why forensic laboratories must often study normal or tumour tissue specimens that are usually archived with this method. The somatic instability of tumour tissue on STR loci and the DNA damages caused by formaldeide are well described. These conditions can cause an incorrect allelic determination that makes a forensic identification fail. In order to evaluate the real incidence of the genetic alterations caused by somatic instability of tumour tissue, and the incidence of the DNA damages caused by formalyn, we studied 25 specimens of patients who have been operated for neoplasia. For each patient, we studied a specimen of fresh tumour tissue and a specimen of formalyn-fixed tumour tissue, and the results of these analyses were compared to a specimen of fresh normal tissue and to a specimen of formalyn-fixed normal tissue of the same patient. D 2005 Published by Elsevier B.V.