Purpose <p>Data on the presentation of behavioral and emotional problems in early childhood and their evolution over time through large, longitudinal cohort studies remain scarce, which limits the current state of knowledge on how to guide early childhood interventions. This study aimed to develop a better understanding of behavior problems in young children with developmental disabilities, of how these change over time, and of associated child and family characteristics.</p> Methods <p>This longitudinal study on 958 families addressed several shortcomings of the literature by adopting an instrument specifically developed to measure behavioral and emotional problems in children with developmental disabilities, the Developmental Behavior Checklist (Einfeld et al. in Manual for the developmental behaviour checklist: Primary carer version (DBC-P) and teacher version (DBC-T), Monash University, 2002), by employing consistent data collection intervals (i.e., after the diagnosis and at two annual follow-ups), and by sampling a homogeneous age group (i.e., 18–59&#xa0;months at the time of diagnosis). Children’s emotional and behavioral problems, adaptive behavior, intellectual functioning, and autism symptoms, as well as parenting stress and family quality of life were assessed.</p> Results <p>Overall, social and communication problems tended to decrease, while externalizing behavior problems tended to increase and internalizing behaviors remained stable over time. Cluster analysis yielded four subgroups based on behavioral and emotional problems as assessed at the time of diagnosis. These subgroups differed in child’s gender and diagnostic labels and on other child and family characteristics. Patterns of change in behavioral and emotional problems significantly differed over time according group membership.</p> Conclusion <p>Co-occuring conditions, such as emotional and behavioral problems, should be considered in planning interventions.</p>