This study aims to describe maternal depressive symptoms (MDS) trajectories in a longitudinal study extending from pregnancy to 27 years after the birth of the firstborn child. We also explored the associations of both MDS trajectories and child internalizing and externalizing problem trajectories with maternal adjustment (adaptive functioning, emotional and behavioral problems). The population-based study was conducted in Tampere, Finland, and the sample comprised 356 first-time mothers. MDS were screened with the Edinburgh Postnatal Depression Scale during pregnancy, first week after delivery, 2 and 6 months postnatally, and when the child was 4–5, 8–9, 16–17, and 26–27 years of age. The internalizing and externalizing problems of the children were assessed with the Child Behavior Checklist when the child was 4–5, 8–9, and 16–17 years of age. Maternal adaptive functioning and internalizing and externalizing problems were assessed with the Adult Self Report at 26–27 years after the birth of the first child. Complete follow-up data were available for 168 mothers. We describe a three-group trajectory model of MDS (High Stable, Low Stable, Very Low). Elevated depressive symptom patterns were associated with less optimal maternal outcomes regarding both adaptive and problem dimensions. The child's internalizing and externalizing problem trajectories were associated with maternal internalizing and externalizing problems but not with maternal adaptive functioning. Maternal and child measures were based on maternal reports only. The interconnectedness of the well-being of the mother and child should be noted in health and mental health services for adults and children. •We present maternal depressive symptom trajectories over 27 years (1989–2017)•The maternal symptom trajectories were Very Low, Low Stable and High Stable•Low Stable trajectory predicted the best and High Stable the least optimal outcome•Child's problems predicted mother's problems but not her adaptive functioning