The interpersonal theory of suicide proposes that severe suicide ideation is caused by the combination of thwarted belongingness (TB) and perceived burdensomeness (PB), yet few studies have actually examined their interaction. Further, no studies have examined this proposal in male prisoners, a particularly at‐risk group. To address this gap, the current study surveyed 399 male prisoners. TB and PB interacted to predict suicide ideation while controlling for depression and hopelessness. High levels of both TB and PB were associated with more severe suicide ideation. The interpersonal theory may aid in the detection, prevention, and treatment of suicide risk in prisoners.