The morbidity and mortality of stab wounds is unknown since much of the data is unobtainable. Folsom Prison, a closed system with respect to population at risk and medical care, represents a unique situation where all stab wounds and subsequent care are accounted for. A retrospective review of stabbing incidents at Folsom Prison identified 751 wounds in 270 prisoners. Overall mortality was 3%. Thirty-five per cent of the victims were hospitalized. The overall chance of serious injury, defined as an assault victim requiring more than cleansing and suturing of his wounds, was 25%. The most common procedures were tube thoracostomy (performed 36 times) and celiotomy (performed 31 times). We believe that this is the first study of its kind involving a closed population to accurately assess the overall morbidity and mortality of stab wounds. The 3% mortality and the 25% requiring a procedure beyond suturing reflects the low injury potential long clinically suspected in stab wounds.