In industrialized countries, the proportion of shift workers is currently estimated to be approximately 20% of the working population. The problem of sleep may be one of the major consequences of shift work. To study the relation between shift work and sleep quality in a female population, 469 nurses at 6 public hospitals in various French regions were interviewed about their working conditions and health in 1980. They were followed up and interviewed again in 1985 and 1990. First, the results showed that nurses had more sleep disorders on alternating schedule including night work at the beginning of the study in 1980, and there was no more association between shift work and sleep quality after 1980. Second, sleep disorders predicted transfer from shift work to day work between 1980 and 1985 and sleep disorders decreased strongly after such transfer. The absence of relation between time schedules and sleep in 1985 and 1990 can be explained by the fact that the follow-up sample was selected, ie, the nurses who continued to work on shift work were able to adapt to it.