Case reports describing different clinical manifestations of IRIS continue to appear, expanding the clinical spectrum of the syndrome. Because the definition of IRIS is one of clinical suspicion and disease-specific criteria have yet to be developed, determining the true incidence will be difficult. Taken together, these studies suggest IRIS may affect a substantial proportion of HIV patients initiating ART. Future epidemiologic and genetic studies conducted within diverse cohorts will be important in determining the importance of host susceptibility and underlying opportunistic infections on the risk of developing IRIS.