We observed seizures resembling infantile spasms in patients with Lennox-Gastaut syndrome (LGS). Infantile spasms, the type of seizures that occurs in patients who have West syndrome, have been well characterized by video-EEG studies and typically occur as a series of sudden generalized flexor or extensor jerks. The seizure types that occur in LGS have not been as clearly delineated. Some patients with West syndrome (WS) in early infancy later develop LGS. Using intensive video-EEG monitoring, we evaluated 14 LGS patients who had seizures that occurred in series. Clinically, the seizures greatly resembled infantile spasms, and the ictal EEG changes were identical to those that occur with infantile spasms. These findings expand the number of features known to be shared by these two syndromes and strengthen the hypothesis that the two syndromes represent age-related manifestations of similar epileptogenic processes.