The challenge of identifying suicide risk in adolescents, and particularly among high-risk subgroups such as adolescent inpatients, calls for further study of models of suicidal behavior that could meaningfully aid in the prediction of risk. This study examined how well the Interpersonal-Psychological Theory of Suicidal Behavior (IPTS)--with its constructs of thwarted belongingness (TB), perceived burdensomeness (PB), and an acquired capability (AC) for lethal self-injury--predicts suicide attempts among adolescents (N = 376) 3 and 12 months after hospitalization. The three-way interaction between PB, TB, and AC, defined as a history of multiple suicide attempts, was not significant. However, there were significant 2-way interaction effects, which varied by sex: girls with low AC and increasing TB, and boys with high AC and increasing PB, were more likely to attempt suicide at 3 months. Only high AC predicted 12-month attempts. Results suggest gender-specific associations between theory components and attempts. The time-limited effects of these associations point to TB and PB being dynamic and modifiable in high-risk populations, whereas the effects of AC are more lasting. The study also fills an important gap in existing research by examining IPTS prospectively.