Context.-Monitoring minimal residual disease by quantitative reverse transcription polymerase chain reaction has proven clinically useful, but as yet there are no Food and Drug Administration-approved tests. Guidelines have been published that provide important information on validation of such tests; however, no practical examples have previously been published. Objective.-To provide an example of the design and validation of a quantitative reverse transcription polymerase chain reaction test. Design.-To describe the approach used by an individual laboratory for development and validation of a laboratory-developed quantitative reverse transcription polymerase chain reaction test for BCR-ABL1 fusion transcripts. Results.-Elements of design and analytic validation of a laboratory-developed quantitative molecular test are discussed using quantitative detection of BCR-ABL1 fusion transcripts as an example. Conclusions.-Validation of laboratory-developed quantitative molecular tests requires careful planning and execution to adequately address all required analytic performance parameters. How these are addressed depends on the potential for technical errors and confidence required for a given test result. We demonstrate how one laboratory validated and clinically implemented a quantitative BCR-ABL1 assay that can be used for the management of patients with chronic myelogenous leukemia.