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Spontaneous movements during induction of anesthesia with propofol were studied in 21 children aged 6-12 yr. The children were randomly assigned to group A (propofol 3 mg.kg-1), B (propofol 5 mg.kg-1), or C (thiopental 5-7 mg.kg-1). A baseline electroencephalogram (EEG) was recorded during 10 min in children awake, supine with eyes closed and opened, and then from the beginning of induction until 5 min after tracheal intubation. Spontaneous movements were observed in all children in group A but only in 14% in groups B and C. The induction EEG sequences were similar for the three groups: after a mean latency of 12 s, the tracing showed an increase in frequency from 9 to 10 Hz (alpha waves) to more than 14 Hz (beta waves). This transition lasted approximately 2 s, followed by delta waves (2-3 Hz) that continued for 1-2 min. Finally, beta waves reappeared and progressively but incompletely replaced delta waves during the next 5 min. Neither spikes, spike-wave patterns, rhythmic theta waves, nor burst suppressions were observed. Spontaneous movements were recorded on videotape and analyzed after the completion of the study by a neurologist unaware of patient treatment. Videotape analysis of the periinduction period showed spontaneous movements to be dystonic and choreiform with flexion, twisting, or extension movements of all extremities. All movements occurred coincident with the appearance of delta waves on the EEG. Their dystonic nature and the absence of EEG abnormalities suggest a subcortical origin and argue against associated cortical epileptic activity.