Mental ill health is prevalent among doctors, especially those in the early stages of postgraduate training. However, a paucity of research has examined factors predictive of psychological distress in this population.To report the findings from a multi-centre survey of mental health among junior doctors in Ireland, and assess the extent to which moderator variables (e.g., age, academic performance, nationality, etc.) alter the levels of psychological distress caused by internship.An online, anonymous, questionnaire was distributed to all interns in the Republic of Ireland in January 2012.A total of 270 interns responded to the survey (45.0 % response rate), with 48.5 % of the respondents having a score indicative of psychological distress. A regression model found that nationality, academic performance, intern training network, rating of work stressors, home stressors, and work-life balance were associated with differing levels of mental health as measured by the General Health Questionnaire-12.There is a need to consider moderator variables when examining mental health in healthcare populations to avoid drawing overly simplistic conclusions. Interns in Ireland reported particularly high levels of psychological distress compared to other studies of mental health among healthcare populations.