Aims: Earlier studies on the associations between parental somatic illnesses and children's psychological wellbeing have focused on the most common somatic illnesses or on specific groups of illnesses. In this study, we aimed to systematically examine whether parental somatic illnesses, diagnosed during an offspring's childhood, are associated with later mental disorders of the offspring and, if so, identify which parental somatic illnesses in particular increase the likelihood for later mental disorders among the offspring. Methods: The 1987 Finnish Birth Cohort study yields longitudinal nationwide follow-up data that include a complete census of children born in a single year. Children have been followed over time through to the year 2012 using official registers maintained by the Finnish authorities. Parental diagnoses of specialised hospital inpatient care were identified from the Hospital Discharge Register after children's birth and followed up until the end of 1995. Children's psychiatric diagnoses from specialised hospital care were identified from the same register for the periods 1996/1998-2012. Logistic regression analyses were used to calculate sex-specific odds ratios for associations of mental disorders with maternal and paternal somatic illnesses using parental death, education, social assistance and psychiatric inpatient care as covariates. Results: Parental somatic illnesses during an offspring's childhood seem to increase the risk for later mental disorders. Several previously unreported somatic parental illnesses were found to be significantly associated with offspring's later mental health. Conclusions: Parental somatic illnesses should be considered as a significant adverse childhood life event, calling for preventive actions and child-centred support in adult healthcare.