The purpose of this study is to examine the relationship between parental religiosity, parental harmony on the subject of religiosity, and the mental health of pre-adolescents. In a community-based sample of 2,230 pre-adolescents (10-12 years), mental health problems were assessed using self-report (Youth Self-Report, YSR), parental report (Child Behavior Checklist, CBCL) as well as teacher report (Teacher Checklist for Psychopathology, TCP). Information about the religiosity of mother, the religiosity of father and religious harmony between the parents was obtained by parent report. The influence of maternal religiosity on internalizing symptoms depended on the religious harmony between parents. This was particularly apparent on the CBCL. Higher levels of internalizing symptoms were associated with parental religious disharmony when combined with passive maternal religiosity. Boys scored themselves as having more externalizing symptoms in case of religiously disharmonious parents. The levels of internalizing and externalizing symptoms in pre-adolescents were not influenced by parental religiosity. Religious disharmony between parents is a risk factor for internalizing problems when the mother is passive religious. Religious disharmony is a risk factor on its own for externalizing problems amongst boys. Parental religious activity and parental harmony play a role in the mental health of pre-adolescents.