The transition to parenthood is often accompanied by depression and stress. Several studies have established risk factors for postpartum depression, e.g., antenatal depression. However, only a few studies have involved fathers. Moreover, most studies focus on the prevalence of depression instead of intraindividual changes over time. Our study investigated differential effects of parental psychopathology and child difficulty on the course of depressive symptoms and feelings of stress for first-time mothers and fathers. Seventy-four mothers and 58 fathers completed questionnaires on depressive symptoms (EPDS) and feelings of stress during pregnancy, and at 1, 3, 12, and 18 months postpartum. Parents rated children's difficulty-fussiness at 3, 12, and 18 months postpartum (ICQ). Parental psychopathology was established during pregnancy using self-reports (SCL-90-R) and anamnestic data. In mentally healthy mothers and fathers depressive symptoms decreased from pregnancy to 18 months postpartum, whereas parents with psychopathology in pregnancy showed a tendency to prolonged depressive phases. In parents with psychopathology, feelings of stress peaked at 12 months postpartum. Child difficulty was associated with elevated levels of psychosocial stress, but only for some participants. Parental psychopathological symptoms during pregnancy should thus be considered as a risk factor for elevated and prolonged depression and elevated psychosocial stress in mothers and fathers across the transition to parenthood.