This paper empirically investigates elder care nurses' negative knowledge. This form of experiential knowledge is defined as the outcome of error-related learning processes, focused on how something is not, on what not to do in certain situations or on deficits in one's knowledge or skills. Besides this definition, we presume the existence of other forms of negative knowledge that relate to elder care nurses' professional competence and practice. Data were collected by means of the prompting-task methodology, which was applied among 37 elder care nurses from a nursing home institution. Content analysis confirmed declarative, procedural, and self-reflective negative knowledge to be relevant in the investigated domain. Additionally, the elder care nurses voiced vicarious negative knowledge. This knowledge was focused on what certain nursing home residents' are not able to do or are not aware of. For each of these forms of negative knowledge, different subfacets are identified and illustrated through sample statements. Moreover, the relationship of different types of workplace errors is outlined. We conclude that negative knowledge represents failure-critical aspects of work situations and, thus, represents a valuable resource for professionals' competence and practice. (Contains 1 table.)