Background: Prior research on adverse experiences in early childhood has mainly focused on at-risk populations while studies of unselected populations are scarce. This topic therefore remains to be elucidated in broader child populations. Accordingly, the aim of this study was to examine if and to what extent children from a general population sample are exposed to psychosocial adversity and stressors in early childhood and whether the development and mental health of children with and without such exposure differ at the age of 18-months. Methods: A random sample of the Copenhagen Child Cohort (CCC2000) comprising 210 children and their parents participated in the study when the children were approximately 18-months. Information on exposures was obtained from a semi-structured interview including the Mannheim Parent Interview (MPI) and classified in agreement with the Multiaxial Classification of Child and Adolescent Psychiatric Disorders (ICD-10), and the Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood (DC: 0-3). Child development was assessed with the Bayley Scales of Infant and Toddler Development – Second Edition (BSID-II), while mental health was measured using the Child Behavior Check List (CBCL 1½-5). Results: Among the 210 children, 91 (43%) had been exposed to psychosocial adversity and persistent stressors. The exposed children differed from the non-exposed children by poorer cognitive development and behavioral regulation, as well as more attention problems and anxious/depressed symptoms. The children exposed to adverse caregiving environments were specifically more likely to have delayed cognitive development than the rest of the sample. Conclusions: In a general population sample of children aged 18-months, exposure to psychosocial adversity and stressors was associated with poorer development and mental health in cognitive and affective domains. These findings highlight an avenue for further research with potential implications for early preventative practices.