Uncertainty exists over the time frame and biological development of cerebral aneurysms. In a new study, Etminan et al. used carbon birth dating to assess turnover of collagen in ruptured and unruptured aneurysms. In all samples, the collagen was on average <5 years old. As carbon levels correlated with patient age and aneurysm size, the authors suggest that this method could be useful for modelling of aneurysm development.