Potato onions (Allium cepa var aggregatum G. Don) are multiplying or aggregating onions, very similar to shallots and have been historically cultivated throughout Europe. Currently in Northern Europe they are maintained in home gardens and ex situ field collections. Potato onions are primarily vegetatively propagated, however in Estonia, near Lake Peipsi, this species has been propagated by seed since the seventeenth century. There is increasing interest in Northern Europe in utilizing this germplasm in organic and/or sustainable farming systems. The genetic diversity and relationship between and within European potato onion collections is unclear. From historical records it is known that cultivation, exchange and trade of potato onion has occurred throughout Europe for hundreds of years. This study utilised molecular markers to assess genetic diversity, duplication of genotypes and relationships among and between Nordic, Baltic, Czech and Croatian potato onion collections. Of 264 accessions, 80 catalogued as unique had identical genotypes with one or more other accessions, and are putative duplicates. The genetic diversity within two Estonian sexually propagated accessions was comparable to that found in all of the vegetatively propagated accessions. Accessions from the Nordic countries grouped together genetically, as did Latvian and Lithuanian accessions. Croatian accessions were genetically separated. These genetic relationships suggest historical movement of potato onion germplasm in North-Eastern Europe. The results, in conjunction with other passport and characterization data, can assist in the development of potato onion core collections, facilitating the conservation and utilization of valuable potato onion genetic resources.