A method of patching a well or a pipe by hydroforming a tubular metal patch. A tool provided with a pair of inflatable packers is inserted inside the patch. The pair of inflatable packers are axially spaced apart from each other by a distance that is substantially equal to the length of the patch. The tool is positioned inside the patch so that the packers are in register with the end portions of the patch. The assembly of the tool and the patch is axially inserted inside the well or the pipe, and positioned in register with the zone for patching. The packers are inflated to a high pressure, sufficient for radially expanding the end portions of the patch and pressing them in a leak-tight manner against the wall of the well or the pipe. The packers are subsequently deflated and the tool is withdrawn. The method is applicable to the oil industry.