Paternal postpartum depression may affect not only the mental health and wellbeing of fathers but their partners and children. We investigated the point and period prevalence of paternal postpartum depression and its association with factors measured during pregnancy in a regional longitudinal study in Nishio City, Aichi Prefecture, Japan, between December 1, 2012, and April 30, 2013. Data were collected once in pregnancy and five times in the first three months postpartum. The Edinburgh Postnatal Depression Scale was used to assess paternal depression, and data were collected in pregnancy on demographic and psychosocial factors. Of 215 fathers who returned at least one of the five postpartum assessments, 36 (17%) reported symptoms of depression in the first three months after birth. In logistic regression analyses, among a number of demographic and psychosocial characteristics that previously had been linked to paternal postpartum depression, only fathers' history of psychiatric treatment and depressive symptoms during pregnancy were associated with paternal depressive symptoms in the postnatal period. The results add to the growing body of evidence on prevalence of paternal postnatal depression and indicate that assessment and support for fathers are important starting in pregnancy. © 2016 Wiley Periodicals, Inc.