Type III Gaucher disease is one of the three recognized subtypes of Gaucher disease, an inherited deficiency of lysosomal glucocerebrosidase. Phenotypically there is a wide spectrum of visceral and neurological manifestations. Enzyme replacement is effective in managing the visceral disease; however, the neurological manifestations remain a more challenging obstacle. There is an unfulfilled need to reliably monitor neurological disease and its response to treatment. A severity scoring tool was developed through neurological domain identification, item generation and tool formation. Domain identification was established based on a retrospective single centre study (n = 15) and a systematic review of publications. Forty-seven patients with neuronopathic Gaucher disease were then assessed using the tool to establish the clinical and statistical reliability of each domain. Judgement quantification of the tool was established through a process of content validity involving five European experts. Content validity is considered to be most effective when undertaken systematically. Concurrent validity and feasibility of the tool was also highlighted. This process allowed a revised and validated version of the tool to be developed.