A cross-sectional household questionnaire survey was conducted along two transects (80 and 45 km long) from Coquimbo and Ovalle cities to the Fray Jorge National Park (FJNP) in the Coquimbo region of Chile in 2005-2007 to investigate the demography of dogs in the context of a study of canine infectious diseases Data were collected on the number of dogs per household, fecundity, mortality, and sex and age distribution The results from 1021 households indicated that dog ownership was common, with a higher proportion of households owning dogs in rural areas (89%), than in towns (63%) or cities (49%) Dog density ranged from 1380 +/- 183 to 1509 +/- 972 dogs km(-2) in cities, from 119 +/- 18 to 1544 +/- 172 dogs km(-2) in towns, and from 10 +/- 04 to 159 +/- 04 dogs km(-2) in rural sites The dog population was estimated to be growing at 20% in cities, 19% in towns and 9% in rural areas The human. dog ratio ranged from 52 to 62 in cities, from 2.3 to 5.3 in towns, and from 1.1 to 2 1 in rural areas A high percentage of owned dogs was always allowed to roam freely in the different areas (27%, 50% and 67% in cities, towns and rural areas, respectively) Observations of free-roaming clogs of unknown owner were reported from a greater proportion of respondents in cities (74%), followed by towns (51%) and finally by rural areas (21%). Overall only 3% of dogs had been castrated In addition, only 29% of dogs were reported to have been vaccinated against canine distemper virus (CDV) and 30% against canine parvovirus (CPV) The higher population size and density, higher growth rate and a higher turnover of domestic dogs in urban than in rural areas and the poorly supervised and inadequately vaccinated dog populations in urban areas suggest that urban areas are more likely to provide suitable conditions for dogs to acts as reservoirs of pathogenic infections (C) 2010 Elsevier BV All rights reserved