Purpose : The purpose of this study was to modify the Paediatric Evaluation of Disability Inventory (PEDI) to create a Pompe disease-specific disability instrument for use in clinical trials and natural history studies. Methods : PEDI item content was revised to include self-care and mobility items appropriate for children and youth with Pompe disease. Data were collected on 30 individuals with Pompe disease (mean age 7.7 - 5.6 years; range 0.4-22.1 years) by parent proxy through telephone interviews. New items were merged with original PEDI items using Rasch rating scale methods. Results : The Pompe-PEDI extended the content range and scoring precision of the original PEDI. Construct validity was demonstrated and test-re-test reliability was excellent. Conclusions : The Pompe-PEDI is a reliable and valid instrument to assess and monitor the functional changes of children and youth with Pompe disease.