This dataset is part of a project on assessment of pain in youth with severe intellectual disabilities. Types of data: 1) Qualitative data (.txt format) on focus groups including caregivers and health professionals of these youths. Focus groups' participants gave their opinion about pain assessment in these youths. 2) Data on self-reported measures (.csv format) that were obtained to validate a questionnaire to assess pain in these youths. 3) Qualitative data (.txt format) on interviews of pain experts, caregivers and health professionals when using a mobile application designed to assess pain in these youths. This data is generated as a result of usability tests of the app. 4) Data on self-reported measures (.csv) that were obtained to test the satisfaction and efficacy of the app in two different times (previous use of the app and post use of the app).