The primary objective of this study was to report on the occurrence of mental health difficulties for a large national sample of Australian fathers of children aged 0-5 years (n = 3,471). Secondary objectives were to compare fathers' mental health against normative data for the general male adult population, and to examine the course of mental health problems for fathers across the early childhood period.Secondary analysis of data from the infant cohort of the Longitudinal Study of Australian Children at three waves when children were 0-12 months, 2-3 and 4-5 years. Comparative data on the prevalence of psychological distress in the Australian adult male population sourced from the National Survey of Mental Health and Wellbeing.Approximately nine per cent of fathers reported symptomatic or clinical psychological distress at each wave, as measured by the Kessler-6. Approximately 30 % reporting distress at wave 1 continued to report distress at a similar or worse level across waves 2 and 3. Fathers not living with their children also had high rates of distress (14 % at wave 1 and 10 % at wave 2). Finally, fathers in the present study had 1.38 increased odds (95 % CI 1.12-1.69) for psychological distress compared with the Australian adult male population.Fathers are at risk of experiencing postnatal mental health difficulties, which may persist across the early childhood period for some fathers. The results suggest routine assessment of fathers' wellbeing should be undertaken in the postnatal period with mental health interventions and support provided across the early childhood period.