We report on the survival and germination of up to a century-old marine protist resting stages naturally preserved in sediments from Koljö Fjord on the west coast of Sweden. This work has focused on germination of dinoflagellate cysts, but diatom resting stages were also observed. We record the longest known survival of dormant dinoflagellate cells. We individually isolated more than 1200 cysts of the three most abundant dinoflagellate taxa: Pentapharsodinium dalei, Lingulodinium polyedrum and Scrippsiella spp. Germination success decreased with core depth, and all successful germinations took place within the first 2 wk of incubation. Pentapharsodinium dalei had the highest germination success rate, with a maximum of up to 80% in 28-yr-old sediment, and could successfully germinate from core sediments dated to 1920 6 12. Scrippsiella spp. cysts with cell contents occurred down to c. 90-yr-old sediment and could germinate from down to ca. 40-yr-old sediments, with a maximum germination rate of 50–60% in recent sediments. Cysts of L. polyedrum germinated frequently down to 20 yr and rarely to c. 80 yr, with a maximum of 20–50% germination success in recent sediments. Cyst isolation under cooled conditions rather than at room temperature resulted in a significantly higher germination success in P. dalei, while no effect was observed for L. polyedrum. The time elapsed since slicing of the core affected survival of L. polyedrum cysts negatively, most likely due to the effect of oxygen. The long-term survival potential of benthic resting stages that we report here has important implications, as viable resting stages accumulated in bottom sediments can be transported back to the water column by, for example, bioturbation and human-mediated sediment dredging. Hence, the sediment may to a higher degree than previously considered play a role as seed bank. This is important in a changing climate and might have particularly severe impacts in the case of harmful species.