Background: This study describes the psychometric testing of the Achondroplasia Personal Life Experience Scale (APLES): a new disease- and functioning-specific health-related quality of life instrument for young people with achondroplasia, which was developed based on the International Classification of Functioning-Children and Youth Version. Method: The qualitative analysis of focus group statements from German patients and parents using the International Classification of Functioning-Children and Youth Version yielded 59 items, which after cognitive debriefing were included in a pilot-test. Psychometric performance was cross-culturally examined in a field- and re-test in Germany and Spain. Results: Cognitive debriefing and pilot-test results suggested to reduce the 59-APLES version to a 35-items version. Field-test data showed acceptable reliability and validity, which further improved after the APLES was shortened to 21 items. Conclusion: Developing a disease-specific instrument within the framework of the International Classification of Functioning allows the universal assessment and comparison of perceived health. Psychometric analysis showed that the APLES fulfills psychometric quality standards and provides a way to assess health-related quality of life from self- and observer report in young persons with achondroplasia. Further studies may use the instrument in clinical research and practice to understand perceived burden and to optimize care. Implications for Rehabilitation Health-related quality of life instruments are useful tools to include in clinical research and/or practice to evaluate treatment effects directly from the patient's perspective. Cross-culturally developed health-related quality of life measures that are based on the International Classification of Functioning Disability and Health provide the opportunity to assess the health status in a standardized language and to compare it across countries and health professions. All four components of the International Classification of Functioning Disability and Health - Child and Youth Version ("Body Functions & Structures", "Activities and Participation", "Environmental Factors", and "Personal Factors") have been shown to be relevant in assessing health-related quality of life and functioning in young achondroplasia patients. Results underline the important aspects associated with disproportionate short stature, emphasizing the benefits of a disease-specific instrument.