The paper describes the development and testing of a paper-and-pencil instrument, the Life Activities Questionnaire for Childhood Asthma, that can be applied to assess activity restriction in children with asthma. It describes how items for the instrument were selected to ensure the validity of the developed instrument. The method by which the reliability of the questionnaire was established is also discussed. The result is a valid and reliable instrument that should have wide applicability in measuring activity restriction because of childhood asthma. The developed instrument has potential use in clinical settings, research, and policy making.