The present study examined the developmental trends of Irritability over the course of adolescence in a italian sample composed by 479 subjects 14 years old at the first time and 20 years old at last time. Three objectives were pursued: 1) identifying developmental trajectories with distinct levels and different pattern of change in Irritability; 2) exploring gender distribution in different trajectory groups; c) finally, determining whether trajectories with different level and trends of Irritability was significantly related to aggressive behaviours and depressive tendencies. Four developmental trajectories were identified. The most part of adolescents were stable at different mean level and only one group (30% of adolescents) decline over the course of time. Each trajectory was associated with different levels of both aggression and depressive tendencies. In particular, the results attest that higher trajectory was characterized by girls and was associated especially with depressive tendencies.