As part of a larger ecologic research project and to collect disease prevalence information on backyard chicken flocks in northwestern Ecuador, 100 randomly selected birds from 10 flocks were examined, and blood, fecal, and ectoparasite samples were collected. The owners of the flocks were surveyed regarding flock management and disease history. Mean flock size was 20 birds (range, 1–75), and birds were kept for eggs and meat for either domestic consumption or local sale. Vaccination rates were low, with most owners (8 of 10) not vaccinating at all and some (2 of 10) vaccinating with one product either sporadically (1 of 10) or annually (1 of 10). None of the owners treated their chickens for parasites. Mortality rates of offspring were reported as high as 50% (range, 35%–50%) per flock. Deaths were associated with diseases described by owners as causing neurologic signs, sudden death, or respiratory problems. In addition, owners described epizootics of wartlike seasonal skin lesions, presumably but not confirmed as avian pox. Results of commercial enzyme-linked immunosorbent assays on serum samples showed that birds had antibodies against infectious bursal disease virus (100%), Newcastle disease virus (97%), avian encephalomyelitis virus (92%), chicken anemia virus (90%), infectious bronchitis virus (85%), Mycoplasma gallisepticum (73%), and Mycoplasma synoviae (68%). Although 11% of birds showed the presence of antibodies for avian influenza, antibody levels were low in all but 4 birds. Most birds (90%) had feather mite infestations. Results of necropsy and fecal examinations found low levels of internal parasitism, with cestodes and ascarids identified as the most prevalent endoparasites. Ectoparasites identified were Dermanyssus gallinae and Ornithonyssus bursa. The poultry diseases to which sampled chickens had been exposed are likely the cause of the high mortality rate reported by flock owners. In these backyard poultry flocks in Ecuador, preventive medicine protocols that provide realistic cost-benefit advantages should be implemented. Because wild birds are susceptible to some poultry diseases, free-roaming chickens might be potential vectors of pathogens that could affect wild birds.