OBJECTIVES: According to the standard three-level format of the EQ-5D, the EQ-5D-Y was developed as "Youth" version, for ages 8-15. Increasingly, it is criticized for ceiling effects and to be overly simplistic. Besides, it is assumed that the EQ-5D-Y do not pick up small changes in health-related quality of life. The study aimed to identify appropriate level labels to develop a four-level (4L) and a five-level (5L) version of the EQ-5D-Y and to test comprehensibility and feasibility of these versions. METHODS: The study was conducted in Germany, Spain, Sweden and UK. Firstly, a pool of possible labels was developed by a literature review and focus group interviews. Using sorting- and response scaling tasks, children and adolescents aged 8-15 rated the severity of the identified labels. Within the second phase, healthy participants aged 8-15 as well as those under treatment for a health condition took part in cognitive interviews (group, individual) to test the extended versions. RESULTS: Each country identified possible labels by a literature review and two focus groups, one with respondents aged 8-10 and one with those aged 11-15 (each with 3-8 participants). Afterwards, 7 to 16 possible new labels per dimension in the different languages were rated in 255 sorting- and response scaling interviews (59-72 interviews per country). About 1/3 of interviews was done in each group: children aged 8-10, 11-12 and 13-15. 140 girls and 115 boys participated. The sample contained respondents with and without a health condition. Each country tested developed 4L and 5L versions by a qualitative approach. The 5L version was identified to be more appropriate and preferred than the 4L. CONCLUSIONS: Study results confirm that an extended version of the instrument is seen as beneficial by the debriefed respondents. Results are the basis for validity testing of the new EQ-5D-5L-Y and for sensitivity testing compared to the EQ-5D-3L-Y.