Objective Preliminary evidence suggests that chronic pain patients complete pain intensity measures using idiosyncratic methods. Our objective was to understand these methods and how they might impact the psychometric properties of the instruments. Design A qualitative focus‐group based study. Setting An academic center in New York City. Subjects Outpatients (n = 36) with chronic low back pain, or neuropathic pain due to diabetes or HIV. Methods Participants were divided into three focus groups based on their pain condition, and asked to discuss pain intensity measures (visual analog and numeric rating scales for average pain over 24 hours; Brief Pain Inventory; and McGill Pain Questionnaire). Audio‐recordings were transcribed and analyzed using an inductive thematic method. Results We discovered four main themes, and five sub‐themes: 1) doubt that pain can be accurately measured (subthemes: pain measurement is influenced by things other than pain, the numbers used to rate pain do not have an absolute meaning, and preference for pain intensity ratings “in the middle” of the scale); 2) confusion regarding the definition of pain; 3) what experiences to use as referents (subthemes: appropriate comparator experiences and the interpretation of the anchors of the scale); and 4) difficulty averaging pain. Conclusions The themes discovered suggest that patients include sensations and experiences other than pain intensity in their ratings, experience the rating of pain as a comparative task, and do not use the scale in a linear manner. These themes are relevant to understanding the validity and scale properties of commonly used pain intensity measures.