AIM: To measure the frequency and content of online social networking among medical students and residents. METHODS: Using the online network Facebook, we evaluated online profiles of all medical students (n = 501) and residents (n = 312) at the University of Florida, Gainesville. Objective measures included the existence of a profile, whether it was made private, and any personally identifiable information. Subjective outcomes included photographic content, affiliated social groups, and personal information not generally disclosed in a doctor-patient encounter. RESULTS: Social networking with Facebook is common among medical trainees, with 44.5% having an account. Medical students used it frequently (64.3%) and residents less frequently (12.8%, p < .0001). The majority of accounts (83.3%) listed at least 1 form of personally identifiable information, only a third (37.5%) were made private, and some accounts displayed potentially unprofessional material. There was a significant decline in utilization of Facebook as trainees approached medical or residency graduation (first year as referent, years 3 and 4, p < .05). DISCUSSION: While social networking in medical trainees is common in the current culture of emerging professionals, a majority of users allow anyone to view their profile. With a significant proportion having subjectively inappropriate content, ACGME competencies in professionalism must include instruction on the intersection of personal and professional identities.