Objectives To describe how evidence from trials and cohort studies may be used to guide choice of test for monitoring patients with chronic disease. Study Design and Setting Exploration of potential criteria for choosing the best monitoring test. Criteria are defined and options for assessment measures for test performance on each criterion discussed. Results Monitoring in clinical practice occurs in three main phases: before treatment, response to treatment, and long-term monitoring. Four important criteria may be used to choose the best test for monitoring a patient in each of these phases. Clinical validity describes the ability of the test to predict the clinically relevant outcome that we are trying to control or prevent. Responsiveness describes how much the test changes in response to an intervention relative to background random variation. Detectability of long-term change describes the size of changes in the test over the long term relative to background random variation. Practicality describes the ease of use, invasiveness, and cost of the test. Test performance generally requires longitudinal data from trial and/or cohort studies using statistical methods such as those discussed. Conclusion Four specific criteria can help clinicians inform evidence-based decisions on which monitoring test to use.