Classically, cerebellar hypermetria observed during fast and accurate movements is ascribed to a delayed onset of the electromyographic activity of the antagonist muscle. We describe here 3 patients presenting a late-onset cerebellar degeneration and exhibiting a hypermetria during their fast and accurate movements in spite of a normal onset latency of the antagonist activity. Hypermetria was found to be due to a slower rate of rise of the antagonist activity.