Although insomnia has been repeatedly linked with suicide ideation, the reason for the linkage is not clear. The Interpersonal Psychological Theory of Suicide (IPTS) proposes that three core variables (thwarted belongingness, perceived burdensomeness, and acquired capability) are the final common pathway for all risk factors for suicide ideation and behavior. Recent research has suggested that insomnia may be associated with suicide ideation independently of the IPTS. We examined cross-sectional data from 151 psychiatric inpatients (ages 12–17) to determine if the association between insomnia symptoms and a continuous measure of suicide risk (measured as increasingly severe ideation and plan) was explained by the framework of the IPTS. When all IPTS variables and depressive symptoms were included in the model, insomnia symptoms did not contribute unique variance to suicide risk. Perceived burdensomeness and depressive symptoms were found to explain the relationship between insomnia symptoms and suicide risk. Our findings suggest that improved sleep might reduce suicide risk, that management of interpersonal need cognitions might reduce risk in the presence of insomnia symptoms, and reinforce the independent role of depressive symptoms in suicide risk in clinical samples of adolescents.