A cross-sectional study was conducted to determine bacterial colonization on the mobile phones (MPs) used by patients, patients' companions, visitors, and health care workers (HCWs). Significantly higher rates of pathogens (39.6% vs 20.6%, respectively; P = .02) were found in MPs of patients' (n = 48) versus the HCWs' (n = 12). There were also more multidrug pathogens in the patents' MPs including methicillin-resistant Staphylococcus aureus, extended-spectrum β-lactamase-producing Escherichia coli, and Klebsiella spp, high-level aminoglycoside-resistant Enterococcus spp, and carabepenem-resistant Acinetobacter baumanii. Our findings suggest that mobile phones of patients, patients' companions, and visitors represent higher risk for nosocomial pathogen colonization than those of HCWs. Specific infection control measures may be required for this threat. Copyright © 2011 Association for Professionals in Infection Control and Epidemiology, Inc. Published by Mosby, Inc. All rights reserved.