OBJECTIVES: To provide international consensus on the competencies required by healthcare professionals in order to provide specialist care for teenagers and young adults (TYA) with cancer. DESIGN: Modified e-Delphi survey. SETTING: International, multicentre study. PARTICIPANTS: Experts were defined as professionals having worked in TYA cancer care for more than 12 months. They were identified through publications and professional organisations. METHODS: Round 1, developed from a previous qualitative study, included 87 closed-ended questions with responses on a nine-point Likert scale and further open-ended responses to identify other skills, knowledge and attitudes. Round 2 contained only items with no consensus in round 1 and suggestions of additional items of competency. Consensus was defined as a median score ranging from 7 to 9 and strength of agreement using mean absolute deviation of the median. RESULTS: A total of 179 registered to be members of the expert panel; valid responses were available from 158 (88%) in round 1 and 136/158 (86%) in round 2. The majority of participants were nurses (35%) or doctors (39%) from Europe (55%) or North America (35%). All 87 items in round 1 reached consensus with an additional 15 items identified for round 2, which also reached consensus. The strength of agreement was mostly high for statements. The areas of competence rated most important were agreed to be: ‘Identify the impact of disease on young people’s life’ (skill), ‘Know about side effects of treatment and how this might be different to those experienced by children or older adults’ (knowledge), ‘Honesty’ (attitude) and ‘Listen to young people’s concerns’ (aspect of communication). CONCLUSIONS: Given the high degree of consensus, this list of competencies should influence education curriculum, professional development and inform workforce planning. Variation in strength of agreement for some competencies between professional groups should be explored further in pursuit of effective multidisciplinary team working.