Exploring psychiatric antecedents in youths at Clinical High Risk for Psychosis (CHR-P) could help understand determinants for early detection and timely care pathways, consequently improving outcomes and prognosis. The aims of this investigation were: (1) to examine the proportion of CHR-P individuals with past contact with mental healthcare services enrolled within a specialized CHR-P service, and (2) to longitudinally compare sociodemographic, clinical, and treatment parameters between CHR-P subjects with and without psychiatric antecedents across 2 years of follow-up. All participants (aged 12-25 years) were recruited within the "Parma At Risk Mental States" (PARMS) program. Across the follow-up, they completed the Health of the Nation Outcome Scale (HoNOS) and the Positive And Negative Syndrome Scale (PANSS). A mixed-design ANOVA and a Kaplan-Meier survival analysis were also used. Of the 170 CHR-P subjects, 95 (55.9%) had previous contact with mental health services. In 85.2% of cases, a care discontinuity was observed. Main psychiatric antecedents were learning disorders (7.4%), anxiety disorder (23.1%), conduct disorder (22.1%), and depressive disorder (14.7%). CHR-P youths with psychiatric antecedents had longer duration of untreated psychosis and a higher 2-year incidence rate of psychosis transition. Having previous contact with psychiatric services also resulted to be a associated with poorer social functioning over time. Carefully monitor mental health suffering and related help-seeking-behavior in youths typically manifested in their early 20's is crucial, also in terms of psychosis prevention. Moreover, special attention should be given to service engagement as care continuity within adolescent-adult transition.