In February 2022, we introduced the innovative new role of mental health nurse clinician (MHNC) in pediatric hematology/ oncology in a pediatric hospital in Quebec with the aim of better addressing the needs of young cancer patients and their families. In two previous articles, we explained the method used to develop the role, as well as the strategy employed to implement it. In this article, we seek to evaluate the effectiveness of the implementation strategy by measuring role feasibility. We will also examine role acceptability and appreciation 1 year following implementation. We asked three groups of participants (adolescents, parents and care providers) to complete a research questionnaire based on the Theoretical Framework of Acceptability (TFA), with good inter-rater reliability and discriminant validity. The questionnaire, which was made available online, consisted of statements with Likert-scale responses (from 1 to 5), as well as open questions. We performed a standard descriptive analysis and used the responses to the open questions to support or add nuance to the quantitative results. In total, 31 healthcare professionals, 10 adolescent cancer patients and 10 parents of adolescent cancer patients filled out the questionnaire. Between February 2022 and February 2023, the MHNC provided a total of 691 interventions to 112 individuals (patients and parents). Follow-up sessions were offered to 61 individuals, and 99.6% of them accepted. We found a very strong correlation (r = 0.96) between the number of hours worked by the MHNC and the number of interventions provided. The vast majority of participants from all three groups agreed that the role is appropriate, appreciated and necessary, and that it brings much-needed clinical expertise in mental health to the department. Care providers, adolescents, and parents indicated that they would request this service again and would recommend it to others, if it were needed. The results, therefore, demonstrate excellent feasibility and high levels of acceptability and appreciation. Our study shows that the implemented MHNC role helps improve the clinical management of the mental health of adolescents with cancer, as well as their parents. The role brings much-needed expertise in psychiatric nursing care and supports the clinical practice of care providers. Another study will be conducted in the near future to measure the effectiveness of the MHNC's interventions.