Background The long‐term psychological/neuro‐psychological sequalae for a minority of survivors of childhood cancer are considerable. This project aims to develop and validate a psychosocial and memory/learning distress thermometer (DT) for paediatric/young adult cancer patients. Methods Pilot/Development Age‐appropriate versions of the DT were developed. A pilot study tested acceptability, usability, and design. Validation Seven collaborating paediatric‐oncology centres with 549 participants validated the DT against Strengths and difficulties questionnaire (SDQ) and Hospital Anxiety and depression scale (HADS) for psychological issues, Utilities Index Mark 2 (HUI2) for memory/learning issues, PedsQL and SF‐8 measured quality of life. Results Using a cut‐off of four, sensitivity against SDQ for under 18 was 75.8%, 18plus against HADS was 94.1%. The specificity was 53.3% against the SDQ for the 18plus specificity against the HADS was 47.1%. The sensitivity against the HUI2 for all age groups was 89.0% specificity was 70.3%. Conclusion The DT is a valid and reliable measure screening instrument. It can be used to identify early on those experiencing psychological distress and memory problems.