The prevalence of ‘tattoo’ skin lesions, characteristic of poxvirus infection, was examined in 339 small cetaceans captured in gillnet fisheries off coastal Peru: 196 Lagenorhynchus obscurus (34.7%, CI 29.0%–41.8%), 54 Delphinus capensis (61.1%, CI 46.6%–74.1%), 77 Phocoena spinipinnis (62.3%, CI 50.5%–73.2%) and 12 offshore Tursiops truncatus (41.6%, CI 15.2%–72.3%). Sexual variation in tattoo prevalence was significant only in P. spinipinnis with males two times more infected than females. Prevalence of poxvirus infection was correlated with the body length class in all species. It peaked around weaning age, supposedly in part due to the loss of maternal protection, and then gradually decreased as immunity developed in the delphinids, but remained high in the porpoise. This pattern is indicative of an endemic infection equivalent to a children’s viral disease. The generalized distribution of the tattoos in several animals suggests that viremia may occur. Indications are that the incidence of the disease in L. obscurus and P. spinipinnis may have increased since 1990, however additional research is needed to confirm this trend.