Tay-Sachs disease is the prototype of lysosomal storage disease. While it was first described over a century ago, the defective enzyme was not identified until 1969, making possible the development of enzyme-based diagnostic and carrier screening techniques. This led to the establishment of the successful international Tay-Sachs screening program, primarily for the high risk Ashkenazi Jewish population. In the past five years the development of recombinant DNA technology has allowed researchers to characterize 95-99% of the mutations causing Tay-Sachs disease in this high risk ethnic group. Knowledge of the exact mutations responsible for the disease coupled with the powerful polymerase chain reaction technique has now made DNA-based screening and diagnosis possible. While the enzyme-based test has proven to be reliable and economical, it cannot differentiate variant phenotypes and requires the presence of specialized testing centers. Although the DNA-based test is presently less economical, it can provide carrier couples with their exact genotype and thus, predict the general phenotype of an unborn child. Furthermore, as the catalogue of mutations leading to human disease increases, more economical DNA methodologies will be developed. In the future it would be expected that a laboratory using a single DNA-based technology could diagnose and screen for a myriad of human diseases including Tay-Sachs disease.