An image encoding/decoding method and apparatus for performing intra prediction are provided. An image decoding method of the present invention comprises deriving an intra-prediction mode for a current block, determining whether or not a left boundary or an upper boundary of the current block is a boundary of a predetermined image region, configuring a reference sample by using at least one reconstructed sample included in at least one reconstructed sample line adjacent to the current block based on the determination result, and performing intra-prediction for the current block based on the intra-prediction mode and the reference sample.