Despite daily interactions by principals with a variety of adults, there is scant research on the experiences which are so disrespectful that they become instances of workplace mistreatment. This study reveals, in a first of its kind, that workplace mistreatment does exist for principals and there are challenges to preventing it. Therefore, the purpose of this article is to confirm the existence of mistreatment in principals' workplaces using the principals' voices to describe their experiences of mistreatment. This study concentrates on adult-on-principal mistreatment across a range, from incivility to mobbing and its relative frequency. The presentation of this qualitative data originates in a mixed-methods study of 12 middle years principals, using two rounds of in-depth semi-structured interviews, plus three quantitative surveys. Parallel data analysis followed by cross data-set comparison was employed. Many adults were perpetrators: parents, teachers, superintendents, school trustees, and more, with particular types of incidents perceived as more frequent than others. While instances were not everyday occurrences, principals identified the provocations for and types of harm caused from such incidents. This study suggests that principals could benefit from professional development regarding dealing with mistreatment at work, as well as a reworking of policies to protect principals from workplace mistreatment. Challenges regarding dealing with mistreatment episodes in a school environment are discussed. Further research is needed as data in this exploratory study are not generalizable over larger populations due to self-selection bias, scope and representativeness of the sample.