Large single crystals of the acentric, tetragonal lithium metaborate, gamma-LiBO2, have been grown using the hydrothermal method. Favorable conditions for the synthesis of gamma-LiBO2 were found over the course of a phase stability study of lithium borates in supercritical aqueous base. Hydrothermal synthesis was achieved by: (1) conversion of the alpha phase, (2) direct crystallization from B2O3 and LiOH or (3) recrystallization of previously crystallized gamma-phase crystallites. Solubility of gamma-LiBO2 in dilute aqueous LiOH was found to be 2-5 wt% from 460 to 75 degrees C with a positive solubility coefficient. Crystal growth experiments were designed to take advantage of the favorable solubility conditions within this range. Seeded growth occurred at a maximum rate of 2.1 mm/day when the dissolution zone temperature was 535 degrees C and the growth zone temperature was 495 degrees C. This permitted the routine growth of centimeter-size crystals in less than I week. These crystals possess an interesting combination of optical properties, including a band gap of about 9eV and high non-linear optical (NLO) susceptibility. (C) 2007 Published by Elsevier B.V.