Neurofibromatosis type 1 (NF1) is a rare, autosomal dominant genetic disorder that is caused by germline mutations in the NF1 tumour suppressor gene, which encodes the tumour suppressor protein neurofibromin 1. Plexiform neurofibromas (PN) are histologically benign nerve sheath tumours, which typically grow along large nerves and plexi. On 5 March 2020, a centralised Marketing Authorisation Application was submitted to the European Medicines Agency (EMA), Marketing Authorisation in EU was granted on 17 Jun 2021. As part of the approval process, a Risk Management Plan (RMP) was developed and submitted to the EMA to summarise the safety concerns emerging from the clinical development program. The RMP included additional pharmacovigilance plans for a noninterventional Post-authorisation Safety Study (PASS) to further characterise the safety of selumetinib in paediatric patients with NF1-related PN in routine clinical practice. The planned non-interventional PASS will address gaps in knowledge identified by the RMP, including the important identified risk and some of the potential risks and missing information on long-term developmental toxicity in children, by characterising the safety profile associated with selumetinib use among paediatric patients (age d 8 to \< 18 years old) with a diagnosis of NF1 with symptomatic, inoperable PN. This study is a specific obligation in the context of a conditional marketing authorisation for selumetinib (ie, Category 2 PASS). Study results will contribute to updating the safety profile of selumetinib in a relatively large population of patients with different personal characteristics across multiple health care systems and patterns of real-world clinical practice in European countries and Israel. The study will enrol 2 cohorts: 1. The Base Cohort includes all enrolled patients aged 3 to \< 18 years. 2. The Nested Prospective Cohort will include the subset of Base Cohort patients aged 8 to \< 18 years who have not reached Tanner Stage V on the index date.