The promise of personalized medicine, namely, that medical products and procedures can be tailored to the individual patient, has not been realized as quickly as some might have thought, although there has been an explosion in the amount of genetic and genomic data collected. The challenge is how to confirm that a particular medical product, such as a drug or a medical device, is safe or more efficacious for one individual based on the particular result of a diagnostic (probably genomic) test. How can diagnostic tests and medical products be co-developed? Several drug-diagnostic or device-diagnostic examples are reviewed and a number of clinical trial designs for co-development are discussed. One instructive project that can illustrate some of the many statistical challenges involving bias and multiplicity is the Microarray Quality Control Project (MAQC). MAQC, now in its second phase, is a unique effort, led by the Food and Drug Administration, which combines the efforts of statisticians, clinicians, and scientists at various federal agencies, industry and academia. A FDA Draft Guidance on In Vitro Diagnostic Multivariate Index Assays (IVDMIAs) is also discussed.