Sixteen subjects affected by Lennox-Gastaut syndrome (11 males and five females, ranging from 5 to 15 years of age [mean age, 9 years 11 months]) were followed for periods of 9 months to 5 years 9 months, and were studied during three to five prolonged hospitalizations for total periods of 2-9 months with a veiw to examining the distribution of epileptic seizures during four states of vigilance, evaluated from a behavioral point of view: sleep, drowsiness, inactive wakefulness, and active wakefulness. it was ascertained that the overall average of 406 seizures daily, directly observed, was distributed as follows: 26 (6.40%) during sleep; 128 (31.52%) during drowsiness; 219 (53.94%) during inactive wakefulness; and 33 (8.12%) during active wakefulness. The comparison between the incidence of seizures observed during active wakefulness and those observed during both drowsiness and inactive wakefulness was significant (p less than 0.001). The latter two states represent, in our study, the shortest period of the day (8 h as compared with the 16 h of sleep and active wakefulness), thus making the results of the comparison even more significant. The results of this study suggest the importance of a stimulating environment for children affected by Lennox-Gastaut syndrome, and they point out that an overdose of antiepileptic drugs, not uncommon in the treatment of this syndrome, may make seizures more frequent.