This study aimed to examine how physical working conditions, psychosocial working conditions and work-family conflicts are associated with sleep complaints, and whether health behaviours explain these associations. We used pooled postal questionnaire surveys collected in 2001-2002 among 40-60-year-old employees of the City of Helsinki (n = 5819, response rate 66%). Participants were classified as having sleep complaints if they reported sleep complaints at least once a week on average (24% of women and 20% of men). Independent variables included environmental work exposures, physical workload, computer work, Karasek's job strain and work-family conflicts. Age, marital status, occupational class, work arrangements, health behaviours and obesity were adjusted for. Most working conditions were associated strongly with sleep complaints after adjustment for age only. After adjustment for work-family conflicts, the associations somewhat attenuated. Work-family conflicts were also associated strongly with women's [odds ratio (OR) 5.90; confidence interval (CI) 4.16-8.38] and men's sleep (OR 2.56; CI 1.34-4.87). The associations remained robust even after controlling for unhealthy behaviours, obesity, health status, depression and medications. Physically strenuous working conditions, psychosocial job strain and work-family conflicts may increase sleep complaints. Efforts to support employees to cope with psychosocial stress and reach a better balance between paid work and family life might reduce sleep complaints. Sleep complaints need to be taken into account in worksite health promotion and occupational health care in order to reduce the burden of poor sleep.