This study traces the developmental course of irritability symptoms in oppositional defiant disorder (ODD) from ages 3-5 and examines the psychopathological outcomes of the different trajectories at age 6. Method. A sample of 622 3-year-old preschoolers (311 were boys), followed up until age 6, was assessed yearly with a semi-structured diagnostic interview with parents and at age 6 with questionnaires answered by parents, teachers and children. Results. Growth-Mixture-Modeling yielded five trajectories of irritability levels for the whole sample (high-persistent 3.5 %, decreasing 3.8 %, increasing 2.6 %, low-persistent 44.1 % and null 46.0 %). Among the children who presented with ODD during preschool age, three trajectories of irritability symptoms resulted (high-persistent 31.9 %, decreasing 34.9 % and increasing 33.2 %). Null, low-persistent and decreasing irritability courses in the sample as a whole gave very similar discriminative capacity for children’s psychopathological state at age 6, while the increasing and high-persistent categories involved poorer clinical outcomes than the null course. For ODD children, the high-persistent and increasing trajectories of irritability predicted disruptive behavior disorders, comorbidity, high level of functional impairment, internalizing and externalizing problems and low anger control at age 6. Conclusions. Irritability identifies a subset of ODD children at high risk of poorer longitudinal psychopathological and functional outcomes. It might be clinically relevant to identify this subset of ODD children with a high number of irritability symptoms throughout development with a view to preventing comorbid and future adverse longitudinal outcomes.