- BACKGROUND: Sleep duration has been associated with overall health status, health behaviours, and mortality. Little is known about habitual longitudinal patterns of sleep in the general population. Furthermore, evidence about whether sleep duration has declined in recent years is contradictory. DATA AND METHODS: The study was based on 8,673 adults aged 18 or older in 2002/2003 (cycle 5 of the National Population Health Survey) and used five self-reported biennial measurements of sleep duration spanning eight years. Multiple distinct trajectories of sleep duration were estimated using latent class growth modeling. RESULTS: Four modelled trajectories of sleep duration were identified: short (11.1% of the population); low-normal (49.4%); high-normal (37.0%); and long (2.4%). The short, low-normal and high-normal sleep trajectories each exhibited a slight linear decline in hours of sleep over the eight years of follow-up. Poor sleep quality was predictive of trajectory group membership and associated with a decrease in sleep duration for three of the four groups. Age and sex were also significant predictors of trajectory group membership. INTERPRETATION: Trajectory analysis is a useful descriptive tool in the investigation of sleep duration over time.