This review highlights the contribution of the cytopathologist in the diagnosis of infectious diseases, with emphasis on the detection and identification of microorganisms in various cytologic specimens. Morphological analysis of the main bacteria, parasites and mycoses observed in cytologic specimens, as well as the cytopathogenic effects of the viruses are discussed. The differential diagnosis (contaminants and exogenous or endogenous foreign bodies) is discussed. Finally, the main pathogens noted in each specimen are briefly reviewed.