The protozoan Neospora caninum is the cause of reproductive diseases in some species of domestic animals that results in severe economic losses to livestock production. These diseases might be transmitted by infected females to their offspring or from oocysts eliminated within the feces of the definitive hosts. The objective of this study was to determine the occurrence of serum antibodies of N. caninum in sheep maintained on farms located in northern Paraná, Brazil. Serum samples were obtained from 381 sheep and 25 dogs that were maintained in 11 farming units to detect the presence of anti-N. caninum antibodies by using the indirect immunofluorescence assay (IFA); titers of antibodies that were ? 50 were considered as positive. The results from this study demonstrated that 13.91% of sheep (10.7% < CI 0.95% < 17.9%) and 36% (18.7% < CI 0.95% < 57.4%) of dogs were seropositive to N. caninum. Further, significant differences were observed when the association between the serology results of sheep and two variables were compared: the slaughter of animals within these units (P = 0.0041; OR = 5.27) and the access of dogs to the viscera of slaughtered animals (P = 0.0001; OR = 1.49). These results confirmed the epidemiological importance of the domestic dog relative to the dissemination and maintenance of N. caninum with an environment.