Gaucher disease (GD) is an inherited lysosomal storage disorder due to deficiency of glucocerebrosidase. Diagnosis of GD may be suspected based on clinical symptoms and confirmed by the analysis of glucocerebrosidase in total white cells, mononuclear cells, fibroblasts and dried blood on filter paper. Low enzyme activities should be followed by molecular analysis of the GBA gene. Although there is no obvious genotype-phenotype correlation, the presence of p.N370S protects from neurological involvement whereas homozygosity of p.L444P mostly leads to a neuronopathic form of GD. Progressive storage of glucosylceramide in mononuclear cells and macrophages results in elevated levels of chitotriosidase and CCL18/PARC which may be used as biomarker to assess disease severity and efficacy of treatment. Chitotriosidase activities cannot be analysed in at least 6% of GD patients due to a null mutation in the corresponding gene.