Objectives: The main objective of this study was to evaluate the contribution of knowledge, religiosity, fear, quality of life, blood donation of peers and sociodemographic and behavioral variables in the practice of blood donation in a representative sample of the population of primary healthcare users in the city of Ribeirão Preto, São Paulo. As specific objectives, a Portuguese version of the Blood or Injection Fear Scale (BIFS) was proposed and an instrument for the evaluation of knowledge about blood donation in the Brazilian population denominated Blood Donation Knowledge Questionnaire (BDK-Brazil) was developed. The metric properties of these instruments were also evaluated. Methods: This was a crosssectional study with randomized stratified sampling. The 41 healthcare facilities of the municipality were grouped into 12 strata, according to the geographic area and the Paulista Social Vulnerability Index. The sample size calculated for the study was 1,054 interviews. Participants answered questions about the blood donation practice, knowledge about donation, religiosity, fear, quality of life and sociodemographic and behavioral variables. To address the main objective of the study the data were included in a structural equation model and the blood donation practice was considered the dependent variable (central construct). The structural model was evaluated through polychoric correlation matrix. The fit of the model was analyzed considering the goodness of fit indices and the significance of the causal paths (β), evaluated by the z-tests, considering a level of significance of 5%. Results: Blood donation was more frequent in males and among individuals with higher socioeconomic and educational level. Among those who never donated blood, higher frequencies of female participants, younger, lower socioeconomic level, single and non-religious were detected. In the structural model, the variables fear, knowledge and sociodemographic variables age, sex, socioeeconomic and educational level were significant. Conclusion: The results of our study suggest the association of the blood donation practice with fear of blood, injections and vasovagal reactions, knowledge and