An epidemic of Pseudomonas aeruginosa folliculitis occurred in 117 persons. An indoor swimming pool at a dude ranch was the source of the infection. Recognition of the epidemic occurred through four patients who reported to our clinic with a characteristic syndrome of follicular pustular eruptions and associated symptoms. Inadequate disinfection of the water was causative. Many affected persons had prolonged contact with the organism because swimsuits were worn for several hours after exposure. Early diagnosis and epidemiological investigation are important in treating this disorder.