Lysosomal diseases are severe genetic enzymopathies generally affecting the child, with a progressively fatal issue in the first few years of life. The group is very heterogeneous regarding: the number of included affections (about 30), as well as the clinical, biological and molecular manifestations. The responsible genes for the respective enzyme deficiencies are located or cloned and the recently developed research allows to characterise the causal mutations and to elucidate the involved molecular mechanisms. In the absence of an efficient therapy a reliable prenatal diagnosis can be proposed. However, therapeutic prospects concerning substitutive therapy, bone marrow transplantation and, in a more long-term, gene therapy are encouraging.