Down-hole tools used for drilling oil and gas wells are subjected to harsh environments where abrasive fluids, high loads and speeds, and high temperatures can cause tool components, including thrust bearings, to quickly fail. This paper discusses the advantages that polycrystalline diamond can provide when used as a bearing material in down-hole tools. Laboratory test results are presented that can be used to help predict the performance of polycrystalline diamond bearings in these down-hole applications. Results from two types of tests are presented including tests that measure bearing capacity and those that evaluate diamond-bearing wear rates. Bearing failures, generated during laboratory testing, are discussed. These failures are very similar to those observed in down-hole drilling tools and indicate that thermal damage to the polycrystalline diamond structure is the main cause of bearing failure. Bearing wear rates measured during laboratory testing show that polycrystalline diamond thrust bearings can provide a long-lasting bearing solution for down-hole drilling tools.