Background:. Suicidal ideation is common in young people. Assessment and monitoring can help to understand its dynamic nature and inform treatment planning. Aims:. The aims were to evaluate psychometric properties of a brief screening tool - the Youth Suicide Ideation Screen-3 item (YSIS-3) and determine its correlation with the Suicidal Ideation Question-Junior (SIQ-JR) and measures of depressive and anxiety symptoms a. Method:. Cronbach's alpha (α) was used to evaluate internal consistency of the YSIS-3 in 1107 young people. Convergent validity was evaluated using network analysis based on individual item polychoric correlations. Structural equation modelling was used to understand latent constructs; pearson product moment correlations to validate the integrity of the underlying construct. and two-way mixed Intraclass Correlation Coefficient to examine longitudinal stability and Cohen's d to assess sensitivity to change. Results:. The YSIS-3 was found to have internal consistency, convergent validity and criteria validity almost identical to the 15-item SIQ-JR. There was a high correlation (0.91) between the latent factor underpinning YSIS-3 and SIQ-JR. The YSIS-3 was more sensitive to change among those presenting with suicidal ideation at baseline. Conclusions:. The YSIS-3 is a valid measure for the assessment and monitoring of suicidal ideation, and is sensitive to change. This brief measure can contribute to regular monitoring of the presence and nature of suicidal ideation, which when included in comprehensive assessment, will inform the clinical management of those at risk of suicide.