To identify animal-related factors associated with Paget's disease of bone (osteitis deformans), we conducted a case-control study in two geographical areas of Spain characterized by different socioeconomic profiles. The analysis presented here is based on 149 cases and 150 controls, frequency matched by sex, age, study area, and place of residence in youth (urban/rural). From a logistic regression analysis, we found that contact with bovine cattle [odds ratio (OR) = 2.14; 95% confidence interval (CI) = 1.16-3.94], consumption of meat traceable to sick livestock (OR = 2.70; 95% CI = 0.98-7.43), and frequent consumption during youth of brains (OR = 1.77; 95% CI = 1.05-2.98) and other viscera increased the risk for Paget's disease of bone. Contact with bovine cattle and consumption during youth of bovid viscera exhibited a dose-response effect as regards length of exposure and frequency of consumption, respectively. A life-style shared with dogs showed itself to be differentially linked to the disease in one study area. Overall, our results support the hypothesis that various animal species are carriers of etiologic agents of Paget's disease of bone.