The brunt of the human immunodeficiency virus (HIV) pandemic has been borne disproportionately by resource-poor regions of the world, where tropical infectious diseases continue to hold greatest sway. As a result, our understanding of the epidemiological, biological, and clinical interactions between HIV and tropical pathogens has lagged, compared with our understanding of the interactions between HIV and pathogens that are common in the industrialized world. Because of the current rapid expansion of HIV care in the tropics, with increasing resources being made available, an overview of the available data is timely. Tropical protozoa are discussed here; other tropical pathogens are discussed in a related mini-review in this issue of Clinical Infectious Diseases.