Pain has a major impact on health and quality of life. Since the level of knowledge of painful conditions can influence how these are addressed and managed, assessing this knowledge in patients becomes crucial. As a result, it is necessary to have culturally adapted and validated instruments that specifically measure patients’ knowledge of chronic pain management. The objective of this study was to carry out the Spanish cultural adaptation and the validation of the outcome Knowledge: Pain Management of the Nursing Outcomes Classification (NOC) in patients with chronic pain, defined as extent of understanding conveyed about causes, symptoms, and treatment of pain. A three-stage study was designed: 1) translation and cultural adaptation through an expert panel, 2) content validation, 3) clinical validation. This study provides nurses with a Spanish version of this scale adapted to their context, as well as a set of structured indicators to measure patients’ knowledge about chronic pain. The results indicated that the culturally adapted Spanish version of the outcome Knowledge: Pain Management had a high level of content validity (CVI = 0.92), with 27 indicators being distributed between two factors. This version has been shown to be reliable in terms of inter-observer agreement (κ = 0.79) and internal consistency (α = 0.95). In conclusion, Knowledge: Pain Management has been shown to be reliable and valid to measure knowledge of chronic pain.