Seizures may directly cause brain injury by disrupting the structure and function of synapses. Previous studies using in vivo time-lapse imaging have demonstrated an acute beading of dendrites and loss of dendritic spines immediately following status epilepticus, but the effects of brief seizures and the long-term evolution of this dendritic injury are unknown. Here, we examined the effects of seizures of varying durations on dendritic structure over several weeks using in vivo multiphoton imaging with kainate-induced seizures in mice. The degree of dendritic injury was directly dependent on the duration of the seizures, with seizures lasting more than 30min (status epilepticus) resulting in a greater than 75% spine loss. However, even brief seizures (<5min) induced moderate dendritic beading and spine loss. The dendritic injury from brief seizures usually recovered within 2weeks, whereas status epilepticus-induced injury only partially reversed. These studies demonstrate that seizures of all durations may trigger at least transient neuronal injury.