Hands and instruments used by healthcare workers may serve as vectors for the nosocomial transmission of microorganisms. The use of cellular telephones by medical personnel and the associated nosocomial transmission of pathogens have not been thoroughly examined. Findings from our study show that cellular telephones are commonly used by hospital personnel, even during patient contact. One-fifth of the cellular telephones examined in this study were found to harbor pathogenic microorganisms, showing that these devices may serve as vectors for transmission to patients.