Actinomycosis was at one time a common diagnosis in this country. It still is fairly common in some parts of the world. As the numbers of antibiotics and indications for their use have increased, the disease has almost become a medical rarity in the United States. This fact might be thought a paradox in view of the universal presence of the actinomyces organisms in every human mouth. However, it is perhaps not well recognized that the actinomyces are true bacteria, and that they are particularly sensitive to most of the common antibacterials in current usage. These facts have combined to decrease the clinical frequency of the disease as well as effectively reduce the opportunity for securing a satisfactory specimen for laboratory culture in suspected cases. Actinomycosis can present in a variety of forms and may mimic other infections or even neoplasms. The clinical pattern of remission and exacerbation of symptoms occurring in parallel sequence with initiation and cessation of antibiotic administration is a phenomenon which should increase suspicion for actinomycosis in any of its manifestations.