["Relatively little is known about the significance of normal variation in objectively assessed sleep duration and its regularity in children's psychological well-being.", 'We explored the associations between sleep duration and regularity and behavioral and emotional problems in 8-year-old children.', "A correlational design was applied among an epidemiological sample of children born in 1998. Sleep was registered with an actigraph for seven nights (range 3 to 14) in 2006. Mothers (n\u2009=\u2009280) and fathers (n\u2009=\u2009190) rated their child's behavioral problems with the Child Behavior Checklist.", 'Children with short sleep duration had an increased risk for behavioral problems, thought problems, and Diagnostic and Statistical Manual of Mental Disorders, 4th Edition-based attention-deficit hyperactivity problems according to maternal ratings. Based on paternal ratings, short sleep duration was associated with more rule-breaking and externalizing symptoms. Irregularity in sleep duration from weekdays to weekends was associated with an increased risk for specifically internalizing symptoms in paternal ratings.'] Are sleep duration and regularity associated with behavioral problems in 8-year-old children?