Purpose To evaluate interns' perceived preparedness for defined surgical residency responsibilities and to determine whether fourth-year medical school (M4) preparatory courses ("bootcamps") facilitate transition to internship. Method The authors conducted a multi-institutional, mixed-methods study (June 2009) evaluating interns from 11 U.S. and Canadian surgery residency programs. Interns completed structured surveys and answered open-ended reflective questions about their preparedness for their surgery internship. Analyses include t tests comparing ratings of interns who had and had not participated in formal internship preparation programs. The authors calculated Cohen d for effect size and used grounded theory to identify themes in the interns' reflections. Results Of 221 eligible interns, 158 (71.5%) participated. Interns self-reported only moderate preparation for most defined care responsibilities in the medical knowledge and patient care domains but, overall, felt well prepared in the professionalism, interpersonal communication, practice-based learning, and systems-based practice domains. Interns who participated in M4 preparatory curricula had higher self-assessed ratings of surgical technical skills, professionalism, interpersonal communication skills, and overall preparation, at statistically significant levels (P <.05) with medium effect sizes. Themes identified in interns' characterizations of their greatest internship challenges included anxiety or lack of preparation related to performance of technical skills or procedures, managing simultaneous demands, being first responders for critically ill patients, clinical management of predictable postoperative conditions, and difficult communications. Conclusions Entering surgical residency, interns report not feeling prepared to fulfill common clinical and professional responsibilities. As M4 curricula may enhance preparation, programs facilitating transition to residency should be developed and evaluated.