Unexplained features have been observed seismically near the middle (∼1700-kilometer depth) and bottom of the Earth's lower mantle, and these could have important implications for the dynamics and evolution of the planet. (Mg,Fe)SiO ₃ perovskite is expected to be the dominant mineral in the deep mantle, but experimental results are discrepant regarding its stability and structure. Here we report in situ x-ray diffraction observations of (Mg,Fe)SiO ₃ perovskite at conditions (50 to 106 gigapascals, 1600 to 2400 kelvin) close to a mantle geotherm from three different starting materials, (Mg _0.9 Fe _0.1 )SiO enstatite, MgSiO ₃ glass, and an MgO+SiO ₂ mixture. Our results confirm the stability of (Mg,Fe)SiO ₃ perovskite to at least 2300-kilometer depth in the mantle. However, diffraction patterns above 83 gigapascals and 1700 kelvin (1900-kilometer depth) cannot presently rule out a possible transformation from Pbnm perovskite to one of three other possible perovskite structures with space group P 2 ₁ / m , Pmmn , or P 4 ₂ / nmc .