Information from the human genome sequence will eventually alter many aspects of clinical practice. It will increase through our understanding of disease mechanisms, and guide the development of new drugs and therapeutic procedures. In the short term, however, knowledge of the genome will have a profound clinical impact on the diagnostic capability of clinical genetics laboratories. Molecular phenotyping using genetic and genomic information will allow early and more accurate prediction and diagnosis of disease and of disease progression. Medicine will become oriented towards disease prevention rather than efforts to cure people at late stages of illness.