A swallow-tailed hummingbird (Eupetomena macroura) was presented with a history of prostration and inability to fly. After a 2-day hospitalization, the bird died and necropsy findings included diffuse hyperemia of the small intestine serosal and mucosal surfaces and the presence of a small quantity of clear ascitic fluid in the coelomic cavity. Intestinal contents and cardiac blood were collected for microbiologic exams yielding pure cultures of a pigmented strain of Serratia marcescens. This strain was susceptible to gentamicin, enrofloxacin, streptomycin, trimethoprim, and sulfamethoxazole and had intermediate susceptibility to chloramphenicol and resistance to cephalotin. The source of the infection could not be ascertained, but possible contamination of hummingbird feeders could be involved, because the infection seemed to originate from the digestive tract.