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To assess whether lambda waves are elicited by watching television (TV) and their association with demographical and EEG features.We retrospectively compared lambda wave occurrence in prolonged EEG monitorings of outpatients who were allowed to watch TV and in standard EEGs recorded in TV-free rooms. All EEGs were interpreted by the same two electroencephalographers.Of 2,072 standard EEG reports, 36 (1.7 %) mentioned lambda waves versus 46 (32.2%) of 143 prolonged EEG monitoring reports (P < 0.001). Multivariable comparison of prolonged EEG monitorings and standard EEGs disclosed that recordings performed in rooms with a TV (odds ratio, 20.6; 95% confidence interval, 4.8–88.0) and normal EEGs (odds ratio, 3.03; 95% confidence interval, 1.5–6.25) were independently associated with lambda waves. In the prolonged EEG monitoring group, all recordings with lambda waves also had positive occipital sharp transients of sleep.Watching TV likely represents a powerful and previously unrecognized stimulus for lambda waves. Furthermore, this study confirms the benign nature of this EEG variant and its strong association with positive occipital sharp transients of sleep.