This study aimed to investigate the relative and sequential importance of individual and organizational predictors of job stress associated with medical internship work. All medical students who graduated in Norway over 2 years (n = 631) were surveyed and followed up 1 year later at the end of the hospital internship year. The outcome was job stress as a house officer; predictor variables included individual factors at medical school and work-related factors during internship. A total of 371 (58%) responded at both time points. Adjusted predictors of job stress were: vulnerability (neuroticism) personality trait (beta 1.7 [95% CI, 0.94 to 2.5]); perceived recording skills (beta -0.43 [-0.78 to -0.08]); number of hours of sleep when on call (beta -2.3 [-3.6 to -1.0]); and learning environment on the hospital wards (beta -0.56 [-0.82 to -0.30]) (see table 2). The vulnerability trait was especially important among the female interns. The predictors explained 29% of the total variance in the model; personality contributed 16% of the variance, perceived recording skills 4% and the organizational factors measured in the internship year explained 9%. In terms of prevention, both individual factors (personality trait and perceived skills) and organizational work-related factors (sleep deprivation and learning environment on the wards) should be considered.