On the basis of first-principles plane-wave calculations, we investigated the electronic and magnetic properties of various point defects including single Ge and C vacancies, Ge + C divacancy, Ge <-> C antisites and the Stone-Wales (SW) defects in a GeC monolayer. We found that various periodic vacancy defects in GeC single layer give rise to crucial effects on the electronic and magnetic properties. The band gaps of GeC monolayer vary significantly from 0.308 eV to 1.738 eV due to the presence of antisites and Stone-Wales defects. While nonmagnetic ground state of semiconducting GeC turns into metal by introducing a carbon vacancy, it becomes half-metal by a single Ge vacancy with high magnetization (4 mu(B)) value per supercell. All the vacancy types have zero net magnetic moments, except single Ge vacancy. (C) 2016 Elsevier B.V. All rights reserved.