Electron paramagnetic resonance has been used to investigate radiation‐induced point defects in hydrothermally grown single crystals of potassium titanyl phosphate ( KTiOPO4 or KTP). The crystals were irradiated at 77 K with 60–kV x rays. A trapped‐hole center, a Ti3+ center, and a Pt3+ center were observed between 10 and 30 K after the initial 77‐K irradiation. These defects become thermally unstable near 160 K. The trapped hole is localized on an oxygen ion adjacent to a potassium vacancy and has resolved hyperfine interactions with three phosphorus nuclei. The Ti3+ ion is the intrinsic self‐trapped electron center in KTP and has weak hyperfine interactions with four phosphorus nuclei.