The incidence of genetic instability affecting a set of STRs commonly used in forensic DNA analyses was assessed by performing a comparative study on 24 lung carcinomas with paired normal tissue samples. Out of 24 samples, 20 (83%) showed allele drop-out (ADO) in at least one STR locus. Allelic imbalance was detected at all the STR loci analysed. A small-cell carcinoma sample showed loss of heterozygosity (LOH), with complete deletion of one allele, at the D5S818 and D13S317 loci.