OBJECTIVE To analyze the influence of psychosocial and organizational factors relating to adherence to standard precautions for preventing exposure to biological material in hospitals. METHODS A cross-sectional study was conducted among 270 medical and nursing professionals at a university hospital in the municipality of São Paulo, Southeastern Brazil, in 2002. After selection by means of simple random sampling, the participants answered a questionnaire on psychosocial variables in the form of a Likert scale. The construct validity was evaluated using factor analysis and the reliability, by means of Cronbach's alpha coefficient. The association between psychosocial factors and adherence to standard precautions were obtained by means of multiple logistic regression analysis, with backward elimination of nonsignificant variables. RESULTS The scales showed satisfactory validity and reliability (Cronbach's alpha between 0.67 and 0.82). Individual, work-related and organizational factors explained 38.5% of the overall rate of adherence to standard precautions. This overall rate of adherence was significantly associated with being a physician, receiving training in standard precautions at the hospital, downplaying the obstacles to following the standard precautions, taking the job more seriously, having feedback from safety practices and implementing managerial actions to support safety. CONCLUSIONS Individual, work-related and organizational factors together influenced the adherence to standard precautions. Programs for preventing occupational exposure to biological material need to take into account the obstacles to following standard precautions within clinical practice, and to emphasize organizational support policies for safety at work.