Actinomycosis continues to elude the clinician. In only four of 57 patients seen at the University of Iowa Hospitals (and in none of 12 since 1958) the disease was correctly diagnosed on admission. The disease is more common in men, but has no seasonal or occupational predilection. A normal inhabitant of the mouth, Actinomyces israelii acts as an opportunistic infection, usually in association with bacterial invasion. It tends to follow a break in normal mucosal barriers. Fistula and palpable mass are the physical hallmarks, with pain and fever the most frequent symptoms. Definitive identification requires anaerobic culture. Chances for cure are excellent with lengthy antibiotic administration.