This article has briefly introduced the dental clinician to the principles and practical application of diagnostic decision analysis. There are trade-offs and uncertainties in the process of arriving at a diagnosis, but they can be understood and controlled. First, the clinician must understand the significance of disease prevalence and assign to the patient an initial probability of disease being present. The clinician must then determine if further diagnostic measurements or tests are warranted. If so, the appropriate test must be selected, based on the ability of the test to revise the initial pretest probability. When a diagnostic test is positive, the clinician must know the probability that disease is actually present. The clinician must also know the probability that disease is actually present if the test result is negative. The astute clinician will calculate the posttest probabilities before proceeding with a test and will base treatment decisions on test results in accordance with predetermined test and test-treatment thresholds.