OBJECTIVES: To describe the qualitative development of corresponding self-reported and observer reported scales for assessing spasticity-related pain (SRP) experienced by children with Cerebral Palsy (CP). METHODS: The Questionnaire on Pain Caused by Spasticity (QPS) is a newly developed clinical outcome measure designed to assess SRP using corresponding versions that can be self-administered by children (5 - 10 years), adolescents (11 - 17 years), and by parent caregivers (as observers of signs of pain in their children).  Cognitive interviews were conducted to confirm appropriate understanding and the ability of children of various ages and CP severity to provide meaningful responses. RESULTS: Two children, eight adolescents, and 11 parent/caregivers participated in the interview sessions.  Parent/caregivers were able to work with their children to collectively identify the location of their SRP.  Children age 7 and above who could read and had sufficient motor skills for independently self-administering a questionnaire could answer questions about pain severity in relation to specific activities, but were not able to reliably address the frequency or duration of their pain.  Children 5-7 years (and those with more severe CP) who were able to communicate answered the same items but in interviewer-administered format.  Parent/caregivers could report on observed signs of pain in their children but not address the subjective intensity of that pain.  They could, however, report on the frequency of those signs of pain.  Because direct attention and close contact time between parent/caregivers and children with CP varies, parent/caregiver observations of the duration of pain was less reliable. CONCLUSIONS: Direct correspondence of items addressing key concepts (e.g. presence of SRP) can provide an anchor for combining patient reported and observer reported information and relating the various descriptive aspects around the concepts being measured to provide a more complete and richer dataset for compromised populations where assessment is challenging.