Domestic dogs (Canis familiaris) are firmly incriminated as reservoir hosts of zoonotic visceral leishmaniasis. As an increasing number of studies have reported high infection rates with American cutaneous leishmaniasis (ACL) in dogs, it is suggested that they should also be incriminated as reservoir hosts of ACL. The evidence to incriminate dogs as ACL reservoir hosts is reviewed, and we conclude that there is, as yet, only circumstantial evidence to support that claim, one of the reasons being that diagnostic tests (mainly serology) used in the studies underestimate the true rate of infection. We report results from the first large-scale study to measure ACL infection rates using the polymerase chain reaction (PCR). A high prevalence of ACL was detected in blood and bone marrow of dogs surveyed in an area of Peru endemic for Leishmania braziliensis and L. peruviana, providing further evidence for their suspected role as ACL reservoir hosts. However, the relatively low ACL prevalence detected in symptomatic dogs (i.e., dogs with ACL lesions or scars) demonstrated that PCR alone cannot be the diagnostic 'gold standard' for mass screening of samples in epidemiological studies.