The trigonal indium borate In19B34O74(OH)(11) was synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 13 GPa and 1150 degrees C. The crystal structure could be determined by single-crystal X-ray diffraction data collected at room temperature. In19B34O74(OH)(11) crystallizes in the trigonal space group R (3) over bar (Z = 3) with the lattice parameters a = 1802.49(6) pm, c = 1340.46(5) pm, and V = 3.7716(3) nm(3). The structure of In19B34O74(OH)(11) contains alternating B-O T2 supertetrahedra units. The presence of hydroxyl groups was confirmed with vibrational spectroscopic methods such as Raman and IR. Besides H2InB5O10, In19B34O74(OH)(11) is now the second known compound in the system In-B-O-H.