Despite life-long pharmacotherapy for many people affected by lysosomal storage diseases, no data are available on their beliefs about their treatments. Therapeutic options range from disease-specific, with varying levels of effectiveness, to purely supportive. This spectrum is illustrated by the three diseases Gaucher disease type 1 (effective disease-specific therapies), Fabry disease (disease-specific therapies with variable effectiveness), and mucopolysaccharidosis type III A/B (supportive care only). Employing the Necessity-Concerns Framework of the Beliefs in Medicine Questionnaire, we investigated intra- and intergroup variability in adults with Gaucher disease type 1, Fabry disease, and parents of children with mucopolysaccharidosis type III A/B. Participants rated