Data for this report come from a nationally representative probability sample survey of noninstitutionalized adults, aged 18 to 79 years. The survey, conducted in 1979, found that insomnia afflicts 35% of all adults during the course of a year; about half of these persons experience the problem as serious. Those with serious insomnia tend to be women and older, and they are more likely than others to display high levels of psychic distress and somatic anxiety, symptoms resembling major depression, and multiple health problems. During the year prior to the survey, 2.6% of adults had used a medically prescribed hypnotic. Typically, use occurred on brief occasions, one or two days at a time, or for short durations of regular use lasting less than two weeks. The survey also found a small group of hypnotic users (11% of all users; 0.3% of all adults) who reported using the medication regularly for a year or longer. If we include anxiolytics and antidepressants, 4.3% of adults had used a medically prescribed psychotherapeutic drug that was prescribed for sleep; 3.1% had used an over-the-counter sleeping pill. The majority of serious insomniacs (85%) were untreated by either prescribed or over-the-counter medications.