Maintaining sufficient viability is critical to the sustainability of ex situ conserved seed collections. For this reason, accessions are regenerated when viability falls below a predefined threshold. Viability is monitored by determining the germination ability of accessions at predefined time intervals. Optimizing the frequency of these germination tests, in order to avoid waste of resources, is humpered by the scarce availability of data about seed longevity, particularly for material maintained under genebank conditions. Here we report on the analysis of nearby 40,000 germination test results collected for a wide range of crop species over a 25 years period by the centre for genetic resouces, the Netherlands (CGN), where seeds of genebank accessions are dried to 3-7;moisture content and stored for the long term under near vacuum in aluminium foil bags at - 20d C. The results indicate that seed viability is well maintained for the large majority of seed lots during the first 25 years after regeneration as only 3.3;of the monitoring testa revealed below- threshold germination values. It is argued that the majority of these substandard seed lots are due to other causes than seed ageing, including dormancy problems and estimation error in germination testing. For material, maintained under the seed management procedures and storage conditions practiced by CGN, it is therefore recommended to delay the first germination monitoring tests to 25 years after regeneration.