This thesis presents the design and evaluation of a perceptually adaptive rendering system for immersive virtual reality. Rendering realistic computer generated scenes can be computationally intensive. Perceptually adaptive rendering reduces the computational burden by rendering detail only where it is needed. A rendering system was designed to employ perceptually adaptive rendering techniques in environments running in immersive virtual reality. The rendering system combines lessons learned from psychology and computer science. Eccentricity from the user's point of gaze is used to determine when to render detail in an immersive virtual environment, and when it can be omitted. A pilot study and a full study were carried out to evaluate the efficacy of the perceptually adaptive rendering system. The studies showed that frame rates can be improved without overly distracting the user when an eccentricity-based perceptually adaptive rendering technique is employed. Perceptually adaptive rendering techniques can be applied in older systems and enable them to display higher quality environments without reducing interactivity.