With the search for hydrocarbons moving to more extreme environments, including deepwater, one of the challenges associated with cementing is ensuring the long-term integrity and mechanical properties of the cement at high temperatures (HT). To avoid strength retrogression at above 110°C, silica is added to the cement. This makes the hydration process more complex, as initially formed hydration products are replaced by more stable phases over time. The nanostructure and mechanical properties of HT-cured cement were studied. At HT, there was a general coarsening of the nanometer-scale structure of the set cement paste over time, with associated degradation of the properties. The rate of coarsening depended strongly on the initial curing conditions, providing possible strategies for improving the properties and performance of HT-cured cement. This is an abstract of a paper presented at the Offshore Technology Conference 2012 (Houston, TX 4/30/2012-5/3/2012).