Finally, smoking at baseline predicted later sleep problems, such that those who smoked the most were most likely-and those who did not smoke at all were least likely-to develop sleep problems and frequent sleep problems over the four-year period. Notably, among those who did report sleep problems at baseline, girls were more likely than were boys, and Asian adolescents were more likely than were adolescents of other racial backgrounds, to report continued sleep problems four years later. Baseline smoking also predicted continued sleep problems, while those who stopped smoking during the four-year period experienced a reduced risk of continued sleep problems by follow-up in 1993.