This study offers a preliminary examination of the Interpersonal-Psychological Theory of Suicide (IPTS; Joiner 2005) in an adolescent clinical sample. The IPTS offers a nuanced framework that has many conceptual and practical merits. Although this theory has a growing base of evidence among adults, it has yet to be tested in adolescents using direct measures of its central constructs. Participants were 147 adolescents (76.2 % girls) on an inpatient psychiatric unit, who completed measures of key IPTS constructs of thwarted belongingness, perceived burdensomeness, acquired capability for suicide, as well as depression severity, hopelessness, and severity of suicidal symptoms. Our findings were largely consistent with hypotheses derived from the IPTS: perceived burdensomeness, and at a marginal level, thwarted belongingness, were independently associated with current suicidal ideation. The thwarted belongingness by perceived burdensomeness interaction marginally distinguished between adolescents with passive and active suicidal ideation. Acquired capability for suicide was associated with recent suicidal intent. Examination of all three IPTS constructs simultaneously revealed main effects of each construct (with a marginal effect of thwarted belongingness), and interaction effects for thwarted belongingness by perceived burdensomeness, and thwarted belongingness by perceived burdensomeness by acquired capability for suicide in association with suicidal symptom severity. Sex, age, depression severity, and hopelessness were controlled in all analyses. This study offers strong, albeit preliminary, support of the IPTS in a clinical adolescent sample. Assessment of IPTS constructs may be useful in determining persistent risk for suicide attempt. Prospective tests of the theory, and extensions to intervention and prevention should be considered in future IPTS research.