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Background: In clinical practice, children are often asked to rate their pain intensity on a simple 0 to 10 numerical rating scale (NRS). Although the NRS is a well-established measure for adults, no study has yet evaluated its validity for children with chronic pain., Objectives: To examine the convergent and discriminant validity of the NRS as it is used within regular clinical practice to document pain intensity for children with chronic pain. Interchangeability between the NRS and an analogue pain measure was also assessed., Methods: A cohort of 143 children (mean [± SD] age 14.1±2.4 years; 72% female) rated their pain intensity (current, usual, lowest and strongest levels) on a verbally administered 0 to 10 NRS during their first appointment at a specialized pain clinic. In a separate session that occurred either immediately before or after their appointment, children also rated their pain using the validated 0 to 10 coloured analogue scale (CAS)., Results: NRS ratings met a priori criteria for convergent validity (r>0.3 to 0.5), correlating with CAS ratings at all four pain levels (r=0.58 to 0.68; all P<0.001). NRS for usual pain intensity differed significantly from an affective pain rating, as hypothesized (Z=2.84; P=0.005), demonstrating discriminant validity. The absolute differences between NRS and CAS pain scores were small (range 0.98±1.4 to 1.75±1.9); however, the two scales were not interchangeable., Conclusions: The present study provides preliminary evidence that the NRS is a valid measure for assessing pain intensity in children with chronic pain.