A novel hydrothermal oxidative pressure-relief (HOPR) route has been successfully developed for the growth of high-quality bulk ZnO single crystals, using metallic zinc and H2O2 as the raw materials, at 400 degreesC for 20 h in an alkali solvent. X-ray powder diffraction reveals the ZnO crystals have a wurtzite structure. Two typical morphologies of perfect hexagonal pyramidal and hexagonal prismatic ZnO single crystals, and bidirectional adhesive crystals, are identified by scanning electron microscopy analysis. The average size of the single crystals is similar to 1.0 mm in length and similar to 0.2 mm in diameter. Short hexagonal prismatic, novel polygonal layer-like, and nanowire ZnO crystals are also obtained by altering the reaction conditions, such as the reaction time and the speed of pressure release. The growth mechanism is a spontaneous nucleation and self-growth process. This novel HOPR route gives an alternative choice for obtaining well-crystallized ZnO bulk crystals from solution.