With the goal of developing a practical method of performing noninvasive measurements of flow in cerebrospinal fluid (CSF) shunts, transcutaneous thermal convection CSF shunt flow measurement was investigated using dimensional analysis, numerical modeling, and bench testing. Using appropriate manufacturing practices and controls, a microcontroller-based device was designed, constructed, and clinically tested. Flow was detected in functioning shunts nine times in 10 attempts. One test failed due to postoperative edema, and subsequent testing was limited to patients who had not undergone shunt surgery within the previous 2 weeks. On the basis of these data and previous reports, 510(k) clearance was granted by the Food and Drug Administration for detection of flow in CSF shunts. Flow in CSF shunts can be detected noninvasively and cost effectively by using a simple thermal convection system. The positive and negative predictive values of the test are equal to or greater than those of brain imaging and radionuclide shunt studies.