OBJECTIVES: To demonstrate how patient and parent/legal guardian interviews reinforce a conceptual model of pediatric functional constipation signs, symptoms, and impact for inclusion in a Pediatric Functional Constipation Daily Diary (PFC-DD); and to evaluate patient and parent/legal guardian comprehension and usability of the PFC-DD administered via electronic diary. METHODS: Qualitative patient interviews were conducted with pediatric patients who have functional constipation and their parent/legal guardian to determine the most important and relevant signs, symptoms, and impacts associated with the condition, and to evaluate comprehension and usability of the draft PFC-DD.  Concept elicitation (CE) and cognitive interviews (CI) were conducted with the parent/legal guardian of children ages 6 months to < 6 years (CE, n=18; CI, n=11), and with children/adolescents ages 6 to < 18 years and their parent/legal guardian (CE, n=18; CI patient n= 21, parent n=20). RESULTS: For both groups, the predominant sign/symptom concepts reported were: stool consistency changes, toileting avoidance and/or retentive posturing, child report and/or behaviors suggesting abdominal pain, difficulty while toileting (e.g., straining, rectal pain), infrequent bowel movements, and appetite changes. Parents of children ages 6 months to < 6 years also reported abdominal hardness, gas, and soiling.  The predominant impacts reported were limitations in physical activity, emotional and social function, sleep (younger age group only), school participation (older age group only), and coping strategies (e.g., medications/supplements). Results from the CIs indicated no comprehension problems for most items. However, minor revisions (e.g., definition for ‘retentive posturing’) were made to the wording of a few items to improve clarity and appropriate understanding of the concept.  No concerns were raised about the usability of the electronic diary. CONCLUSIONS: Findings support the content validity of the PFC-DD, a new instrument that includes PRO and ObsRO items to assess the key signs, symptoms, and impacts experienced by pediatric patients with functional constipation.