Introduction The current criteria for detecting a Clinical High-Risk (CHR) state for psychosis do not address cognitive impairment. A first step for identifying cognitive markers of psychosis risk would be to determine which aspects of neurocognitive performance are related with more severe psychotic-like symptoms. This study assessed cognitive impairment associated with prodromal symptoms in adolescents receiving public psychiatric treatment. Methods 189 adolescents were recruited from consecutive new patients aged 15–18 attending mainly outpatient adolescent psychiatric units in Helsinki. They had been screened for prodromal symptoms using the Prodromal Questionnaire, and all screen-positives as well as a random sample of screen-negatives were interviewed using the Structured Interview for Prodromal Symptoms (SIPS) and underwent testing using a large, standardized neurocognitive test battery. The sample included 62 adolescents who met the CHR criteria (CHR) and 112 who did not (non-CHR). A healthy control sample (n =72) was also included to provide age- and gender-matched norms. Results The CHR group performed worse on visuospatial tasks than the non-CHR group. Among CHR adolescents, negative symptoms were associated with slower processing speed and poorer performance on verbal tasks. Among non-CHR adolescents, positive symptoms were associated with poorer performance on visuospatial tasks, and negative symptoms with poorer performance on verbal tasks. Conclusion Clinical high-risk status is associated with impaired visuospatial task performance. However, both positive, psychotic-like symptoms and negative symptoms are associated with lower levels of neurocognitive functioning among adolescents in psychiatric treatment regardless of whether CHR criteria are met. Thus, even mild positive and negative symptoms may have clinical relevance in adolescents in psychiatric care. Adolescents with both psychotic-like symptoms and neurocognitive deficits constitute a group requiring special attention.