In this paper catastrophic behavior found in computer systems is investigated. Deterministic Catastrophe theory is introduced first. Then it is shown how the theory can be applied in a stochastic framework, which is useful for understanding computer system performance models. Computer system models that exhibit stochastic cusp catastrophe behavior are then analyzed. These models include slotted ALOHA, multiprogramming in computer systems, and buffer flow control in computer networks. © 1987, ACM. All rights reserved.