para-Menthane-3,8-diol(PMD) is a monoterpene spent product of the distillation of leaves of the Australian lemon-scented gum tree (updated nomenclature Corymbia citriodora ssp. citriodora). In April 2005, the U.S. Centers for Disease Control and Prevention (CDC) endorsed two non-deet mosquito repellents, including PMD. However, few mosquito professionals have in-depth familiarity with the history and efficacy of PMD. In this article, we describe the origin and development of PMD as a repellent and offer a comprehensive review of its performance against Aedes, Anopheles, Culex, and Ochlerotatus. In addition, we present original data from field and laboratory studies involving large numbers of subjects and comparisons with high-concentration deet and other repellents. We conclude that not only is the CDC endorsement warranted but also that it probably underestimates the value of PMD as a deet alternative for public health applications.