Twenty-seven patients who suffered from alcohol dependence syndrome and who were admitted to the Department of Psychiatry at NCNP were investigated for impaired sleep. The incidence of “insomnia night”, when a patient has trouble getting sufficient sleep even after taking additional drugs for insomnia, was used as the index for impaired sleep. “Insomnia night” was observed among 51.9% (14 of 27) of the patients during administration; 18.5% (nine of 27) experienced “insomnia night” only during the withdrawal period. The mean incidence was 3.5 nights of 10 nights for 0–9th day after abstinence and 2.0 nights of 10 nights for 10–19th day after abstinence; 33.3% (nine of 27) claimed “insomnia night” even after the withdrawal period and the highest incidence was the 160–169th day after abstinence, average frequency being 4.4 nights of 10 nights. Impaired sleep emerging after the withdrawal period neared the clinical course of Komiyama's protracted withdrawal symptoms, thus suggesting that it might be one of the protracted withdrawal symptoms.