The temperature of formation of replacement dolomite and δ18O(H2O) of dolomitizing fluid in the Latemar carbonate buildup, Dolomites, Italy, were estimated independently from carbonate clumped isotope thermometry. Dolomite formed at 42–72 ± 9–11 °C (±2 standard deviations, SD) from fluid with δ18O(H2O) that averages –0.3‰ ± 3.3‰ (Vienna standard mean ocean water; ±2 SD). The estimated temperature and δ18O(H2O) are similar to those of modern diffuse flow fluids at mid-ocean ridges, the kind of fluid that has been proposed previously as the dolomitizing fluid in the Latemar buildup, based on the trace element compositions of dolomite. Calcite in limestone preserves original δ18O, but records clumped isotope temperatures, 44−76 ± 9−11 °C (±2 SD), that are higher than those at which the limestone formed. Temperature recorded by calcite, but not δ18O, was likely reset during dolomitization. Clumped isotope thermometry has great potential for application to studies of burial and diagenesis by retrieving independent estimates of temperature and δ18O(H2O) with uncertainties as low as ±5 °C (±2 standard errors, SE) and ± 0.75‰ (±2 SE), respectively, from a single stable isotope analysis of a carbonate mineral.