Background and Purpose: Nosocomial infections are a growing problem in many health centers. Cell phones used by the medical staff can act as a vector for nosocomial transmission of microorganisms. This study aimed to investigate the role of cell phones of senior medical students in the spread of nosocomial bacterial infections in Amir-al-Momenin general hospital in Tehran in September 2015. Methods: Thirty medical students were enrolled using convenience sampling method. Demographic data, perspectives, attitudes, phone type, and frequency of cleaning of mobile phones were collected by questionnaires. Samples were taken from the phones using a sterile swab moistened with a nutritive medium in order to assess the possibility of bacterial growth. Results: A total of 53.3 percent of mobile phones were infected. Isolated bacteria were: Staphylococcus epidermidis (26.7%), Nonalbicans Candida (16.7%), Bacillus PSP (13.3%), Micrococcus PSP (10%), non-hemolytic Streptococcus and Enterococcus (each 6.7%), and Klebsiella and Staphylococcus aureus (each 3.3%). Conclusions: Mobile phones can act as potential carriers of nosocomial infections which are significantly higher in male students' phones and in smartphones. So, some restrictions should be applied to their use in sensitive areas of hospitals. Also, due to the significant impact of cleaning mobile phones in reducing the frequency of bacterial contamination, attention to their regular cleaning should be considered.