Aim: We investigated the associations between clinical high-risk for psychosis (CHR), psychotic-like symptoms and suicidality among adolescent psychiatric patients. Methods: The sample consisted of 54 CHR and 107 non-CHR psychiatric patients aged 15-18 in Helsinki, Finland, who were assessed at the beginning of their psychiatric treatment with the Structured Interview for Prodromal Syndromes (SIPS). Current suicidality was measured with the Beck Depression Inventory (item 9), while lifetime suicidality was evaluated from all available data, including patient files. The participants were followed for 2.8-8.9 years via the national hospital discharge register, with the follow-up outcome being intentional self-harm. Data on suicides were also gathered from the Causes of Death statistics. Results: Only 30.5% of the adolescents had no suicidal ideation at the beginning of their treatment. CHR risk state and SIPS-assessed delusions, suspiciousness, and hallucinations were associated with higher current suicidality. Of the 154 adolescents with register follow-up, there were five (3.2%) with intentional self-harm resulting in hospital treatment, all female. CHR status was not associated with self-harm. Current suicidality, familial risk of psychosis, and SIPS decreased expression of emotions were associated with self-harm during follow-up. In a Cox regression analysis model among girls, only decreased expression of emotions remained a significant predictor of intentional self-harm. Baseline suicidality measures were not associated with transitions to psychosis. Conclusions: CHR status was associated with higher current suicidality but did not predict follow-up intentional self-harm in treatment-seeking adolescents. Decreased expression of emotions may indicate higher risk of intentional self-harm in adolescent treatment-seeking girls.