Emergency physicians are often required to evaluate and treat undifferentiated patients suffering acute hemodynamic compromise (AHC). It is helpful to apply a structured approach based on a differential diagnosis including all causes of AHC that can be identified and treated during a primary assessment. Tension pneumoperitoneum (TP) is an uncommon condition with the potential to be rapidly fatal. It is amenable to prompt diagnosis and stabilization in the emergency department. We present a case of a 16-year-old boy with TP to demonstrate how TP should be incorporated into a differential diagnosis when evaluating an undifferentiated patient with AHC.