AIM: Sleep problems in the second 6 months of life are common and associated with maternal depression. This paper extends previous research to (i) establish the prevalence of sleep problems in younger infants from a broader socio-economic spectrum, (ii) examine the relationship between infant sleep problems and maternal physical, as well as mental, health, and (iii) explore mothers' sleep quality as a potential mediator of this relationship. METHODS: DESIGN: Cross-sectional, community survey in Melbourne, Australia. SAMPLE: Mothers of 3- to 6-month-old infants (mean 4.6 months) recruited from well-child clinics in six sociodemographically diverse metropolitan local government areas. OUTCOME MEASURES: Maternal mental and physical health; standardised questionnaire on infant sleep patterns; maternal report of an infant sleep problem (yes/no). RESULTS: The survey was completed by 692 mothers; 237 (34%) reported an infant sleep problem, of whom 73 (31%) rated the problem as severe. Sleep patterns characterising a problem included the infant waking seven nights per week, nursing the infant to sleep at the beginning of the night, the infant sleeping in the parent's room, and parental disagreement regarding managing infant sleep. There was no relationship between sleep problems and socio-economic levels. Mothers reporting infant sleep problems had poorer mental and physical health compared with those not reporting sleep problems. CONCLUSION: Sleep problems are common in early infancy across metropolitan socio-economic levels and are associated with poorer maternal health and well-being. Preventive strategies for infant sleep problems need to begin early in primary care to improve mothers' health.