The survival of hibernating adults was assessed in its winter habitat in the Netherlands to gain insight in the potential importance of this life-history phase for the population dynamics of this endangered sp. Compared to other odon., monthly survival rates (Dec. 2004 – March 2005) were high (mean ± SE = 0.75 ± 0.08), but overall winter survival was low (0.42). Potential causes of mortality during hibernation are discussed. The results imply that effective protection of this sp. in the Netherlands may benefit from protection of both its breeding and wintering habitat.