next generation dna sequencing promises to revolutionize clinical medicine and basic research . however , while this technology has the capacity to generate hundreds of billions of nucleotides of dna sequence in a single experiment , the error rate of approximately 1 % results in hundreds of millions of sequencing mistakes . these scattered errors can be tolerated in some applications but become extremely problematic when “ deep sequencing ” genetically heterogeneous mixtures , such as tumors or mixed microbial populations . to overcome limitations in sequencing accuracy , a method duplex consensus sequencing is provided . this approach greatly reduces errors by independently tagging and sequencing each of the two strands of a dna duplex . as the two strands are complementary , true mutations are found at the same position in both strands . in contrast , pcr or sequencing errors will result in errors in only one strand .