Abstract: Purpose: The translation of genome sequencing into routine health care has been slow, partly because of concerns about affordability. The aspirational cost of sequencing a genome is 1000,butthereislittleevidencetosupportthisestimate.Weestimatethecostofusinggenomesequencinginroutineclinicalcareinpatientswithcancerorrarediseases.Methods:WeperformedamicrocostingstudyofIllumina−basedgenomesequencinginaUKNationalHealthServicelaboratoryprocessing399samples/year.Costdatawerecollectedforallstepsinthesequencingpathway,includingbioinformaticsanalysisandreportingofresults.Sensitivityanalysisidentifiedkeycostdrivers.Results:Genomesequencingcosts£6841percancercase(comprisingmatchedtumorandgermlinesamples)and£7050perrarediseasecase(threesamples).Theconsumablesusedduringsequencingarethemostexpensivecomponentoftesting(68–721000/genome in a single laboratory. This aspirational sequencing cost will likely only be achieved if consumable costs are considerably reduced and sequencing is performed at scale