Negative expertise is conceptualised as the professional's ability to avoid errors during practice due to certain cognitive agencies. In this study, negative knowledge (i.e. knowledge about what is wrong in a certain context and situation) is conceptualised as one such agency. This study compares and investigates the negative knowledge of elder care nurses at three different levels of professional experience. Thereby, various forms of negative knowledge—declarative, procedural, self-reflective and vicarious—are investigated. Moreover, the specificity of negative knowledge is compared across different levels of professional experience. Verbal data was collected from a prompting task study of 37 elder care nurses. These were prompted 20 diagnoses of varying typicality for the professional field. The nurses were asked what was critical to pay attention to and what ought to be avoided in case of these diagnoses. The study's results reveal a significant superiority of highly tenured elder care nurses in vicarious negative knowledge, as well as in highly specified negative knowledge. Procedural and procedural negative knowledge (PNK)—which are the most important facets in quantitative terms—show an approximately parallel developmental pattern among the different groups. For declarative knowledge, a U-shaped intermediate effect was discovered. It is concluded that PNK has the most immediate error-preventive function. With regards to future research, the great specificity of highly tenured elder care nurses' negative knowledge discovered in this study is discussed here as one possible explanation as to why they are able to intentionally avoid errors (i.e. their negative expertise).