Objectives: Adherence to treatment has proven to require the involvement of patients in treatment and care planning. This process involves incorporating patient knowledge, or knowledge about the patients’ everyday life, into the clinical encounter. This article explores the disclosure practices of such knowledge from older adults with multimorbidity. Methods: This was an 18-month qualitative study among 14 older adults with multimorbidity living in Denmark. A thematic analysis was applied, focusing on perceptions of patient knowledge and disclosure practices among the participating patients. Results: Older adults with multimorbidity have various reasons for not disclosing personal knowledge. The results present three different domains of what we termed discarded patient knowledge: (1) knowledge that had no direct biomedical relevance from participants’ perspective; (2) knowledge considered too private; and (3) knowledge assumed to position one as inferior. Discussion: The participants made judgments on what they believed was welcome in the clinical encounter, framing their knowledge within the purview of biomedicine. Participants’ disclosure practices showed that personal knowledge is sometimes not recognized as important for health and care by participants themselves. Knowledge that could have influenced practitioners’ understanding of the problem and provided different solutions, is argued to be discarded patient knowledge.