This monograph includes five chapters about neurofibromatosis type 1 (NF1), a condition characterised by changes in skin colouring and the growth of tumours along nerves in the skin, brain, and other parts of the body. Chapter One concerns the evolving molecular biology, targeted therapeutics, and neurocognitive deficits in neurofibromatosis type one. Chapter Two focuses on gastrointestinal stromal tumours and reviews the clinicopathologic features of these tumours and discusses differential diagnostic considerations. Chapter Three explores juvenile myelomonocytic leukaemia, a rare haematological malignancy of the paediatric population, and its association with NF1 and distinguishing features in this context. Chapter Four reviews molecular approaches for the diagnosis of NF1, from single-gene testing to next-generation sequencing of gene panels, with a focus on the issues of sensitivity and variant interpretations. Finally, Chapter Five focuses attention on focal cortical dysplasia that has been identified in the population of NF1 patients that have had coexistent hippocampal sclerosis.