To test whether Australians in utero during the Southern hemisphere flu peak would show increased suicidal and depressive symptoms, as would those born in the Northern hemisphere and who were in utero during the Northern hemisphere flu peak. A sample of 2514 adolescents and young adults presenting to general practitioners completed measures of depressive and suicidal symptoms. Patients' date and country of birth were recorded. Those born in the Southern hemisphere in September-November showed the highest suicidal and depressive symptoms, as did those born in the Northern hemisphere in March-May. Season of birth may be a risk factor for depressive and suicidal symptoms.