Inter-simple sequence repeat (ISSR) polymorphism was used for finding markers linked to the Ns gene, responsible for a resistance of potato (Solanum tuberosum L.) to potato virus S (PVS). The ISSR markers UBC811660 and UBC811950 were found to be linked to Ns. Linkage distances were estimated to be 2.6 cM and 6.6 cM, respectively. UBC811660 showed high accuracy for detection of PVS resistance in diploid potato clones. In tetraploids, among seventeen studied genotypes containing the resistance gene, this marker was revealed in eleven. UBC811660 can be a powerful tool for detection of genotypes carrying the Ns gene in diploid potato breeding programmes.