['Most studies on the effects of early risk factors on future mental health focus on specific obstetric complications as risk factors for specific disorders. However, obstetric complications rarely occur in isolation, and the same holds for psychiatric problems.', 'To study prenatal and perinatal risk factors for psychiatric multimorbidity in early adulthood and to determine whether these differ from risk factors for monomorbidity.', 'Monomorbidity and multimorbidity of six types of psychiatric disorders were determined by a standardised psychiatric interview. Using univariate and multivariate logistic and ordinal logistic regression, associations of mono- and multimorbidity with prospectively collected early risk factors were examined.', 'Two hundred and eighty-five young adults selected from a prospective birth cohort on the basis of their Obstetric Optimality Scores.', 'Six types of psychiatric disorder and their co-occurrence.', 'Monomorbidity was related to isolated early risk factors such as low birth weight or a low Apgar score, and to an accumulation of unfavourable pre- and perinatal events. Multimorbidity on the other hand, was only related to a chain of pre- and perinatal adversities.'] Is psychiatric morbidity related to a chain of prenatal and perinatal adversities?