Stress has been reported among Swedish social workers for over a decade. Survey data from a longitudinal quasi-experimental trial in the public sector of reduced working hours, with a proportional decrease in workload and retained full pay, were used to examine the effect on stress, symptoms of Exhaustion syndrome, psychosocial work characteristics and work–life balance in social workers. Reduced working hours had a positive effect on restorative sleep, stress, memory difficulties, negative emotion, sleepiness, fatigue and exhaustion both on workdays and weekends; on sleep quality on weekends; and on demands, instrumental manager support and work intrusion on private life.