Objectives: The aim of this study was (1) to explore in detail the working load of teachers, (2) to analyse the extent of negative or threatening school-related events teachers are confronted with, and (3) to evaluate mental health strain by applying the general health questionnaire (GHQ). Methods: A sample of 949 teachers in 10 grammar schools (German: Gymnasien) and 79 secondary modern schools (German: Hauptschulen) was investigated applying (1) a questionnaire covering different aspects of the occupational burden and threatening school-associated events and (2) the general health questionnaire (GHQ-12). Results: Based on what teachers indicated in the questionnaire, full-time teachers work more than 51 h weekly. More than 42% of our sample indicated verbal insults, almost 7% deliberate damage of personal belongings, and 4.4% threat of violence by pupils during the past 12 months. When applying the GHQ-12, we found that 29.8% of the sample report significant mental health problems. With respect to school types, teachers in secondary modern schools indicated more of such problems, while no effects regarding age, gender, or full/part-time teaching were observed. Conclusions: To be a teacher is a hard work and requires coping of considerable amount of adverse events. Based on the GHQ, nearly 30% of teachers suffer from significant mental health problems.