Fabry disease is a lysosomal storage disorder with an X-linked pattern of inheritance. Fabry disease is caused by impaired degradation and accumulation of the glycosphingolipid globotriaosylceramide, due to a deficiency of the enzyme α-Galactosidase A. Both males and females can be affected, although in general, females demonstrate a more attenuated phenotype. Screening and individual diagnostic testing revealed a higher prevalence than expected of individuals with variants in the Fabry gene. However, while these individuals may have Fabry disease, a variant in the Fabry gene may also be non-pathogenic. This caries the risk of misdiagnosis, inappropriate counseling, and unjustified treatment with expensive enzyme replacement therapy. The aim of this thesis was to improve the diagnosis of Fabry disease, in order to support the diagnostic process in individuals with a genetic variant of unknown significance in the Fabry gene. A literature review on screening for Fabry disease showed that a large number of individuals with a non-specific clinical feature such as cardiac hypertrophy, chronic kidney disease of stroke, do not demonstrate characteristic signs or symptoms as seen in classical Fabry disease. In collaboration with (inter)national experts on Fabry disease we developed diagnostic guidelines to aid in the diagnostic approach for these individuals, using the best available evidence from the literature and additional analyses. Furthermore, we specifically studied the diagnostic value of clinical and biochemical features characteristic of classical Fabry disease.