Background and objective: Brucellosis is primarily a contagious disease of domestic animals causing abortion, so it is considered one of the most serious of the current public health problems, especially in developing countries. The main purpose of this study was finding the incidence of human and animal brucellosis and detection of any correlation between human and animal brucellosis in Khoy, one of the endemic regions in Iran.Materials and Methods: We carried out an ecological study in Khoy district in North West of Iran. We ascertained all new cases of human and animal brucellosis in the 2001-2004 period. Data were analyzed using Pearson correlation coefficient (r) and square of correlation coefficient (r2). Seasonal incidence was calculated for each species.Results: The cumulative incidence rate of human brucellosis was detected to be 175/100,000, cattle brucellosis was 391/100,000, and sheep and goat brucellosis was 105/100,000. We detected direct and incomplete correlation between human and cattle (r=0.096, r2=0.009, p value 0.742), human and sheep (r=0.267, r2=0.071, p value=0.355), and cattle and sheep (r=0.797, r2=0.635, p value=0.001).Conclusion: The most effective routes to control the disease include pasteurization or boiling of milk for human consumption, cooking all food stuff derived from animal sources, vaccination of cattle against brucellosis, isolation and slaughtering of seropositive reactors for brucellosis and providing protective clothing for humans dealing with infected cattle.