BACKGROUND: The residency is a critical period for doctors to establish their professional identity and ethical standards, and yet during this time, residents are susceptible to engage in a diverse range of unprofessional behaviors. To prevent the misconduct of residents, it is critical to have a thorough understanding of the contributing factors or circumstances. METHODS: We conducted a qualitative study on 20 residents at one Korean university-affiliated tertiary hospital. During in-depth interviews, residents were asked to reveal their experiences or observations of misconduct, and describe their perceptions on the attributes of professional lapses. RESULTS: Diverse unethical and unprofessional behaviors were extracted from the transcripts and reported in a previous paper. In the current paper, the attributes that residents regarded as the causes of their unprofessional behaviors were identified within four categories: (1) inadequate systems within training hospitals; (2) lack of professionalism education; (3) strong hierarchical structure; and (4) poor character of individuals. The residents tended to perceive their misconduct as situation-sensitive, and emphasized the importance of systematic and cultural changes. CONCLUSIONS: To enhance medical professionalism among residents, the results of this study suggest the need of systematic and structured training programs, adequate professionalism education with clear codes of conduct, and active monitoring and feedback systems.