The purpose of this study was to examine the correlation of medical incidents and errors among nurses with factors describing their lifestyle, health, and work environment. We analyzed questionnaires completed by 6,445 female hospital nurses engaged in shift work in Japanese hospitals with general wards of more than 200 beds. Logistic regression analysis indicated that the risk for medical incidents/errors was predicted by being under treatment, absence due to sickness in the past 6 months, workplace, break times during night shift, bodily pain, and role (emotional). These results indicate that to prevent the occurrence of medical incidents/errors, it is necessary to regard current/recent illness, bodily pain, and role (emotional) as a nurse’s personal problems and break times during the night shift and workplace as administrative problems.