A cutting guide for periacetabular osteotomy comprising: - at least a first main body having a longitudinal opening defining a cutting line for the insertion of a cutting instrument, extending from a first end to a second end of said first main body; said first main body has a first portion extending from said first end to an intermediate section, and a second portion (2") extending from said intermediate section to said second end; - at least two positioning and fixing arms (4a, 4b) extending away from said first main body from opposite sides with respect to said longitudinal opening, in order to correctly position said first main body on a bone and fix it thereto through respective fastening members; both the first main body and the positioning and fixing arms (4a, 4b) having a lower surface adapted to be coupled to the patient's bone, shaped on the anatomy of the patient's bone to enable the correct and univocal positioning thereof, such that the lower surface is the negative of the surface of the bone to which the first main body must be coupled; - a second main body having a longitudinal opening defining a cutting line for the insertion of a cutting instrument, extending from a first end to a second end of said second main body; said second main body having a first portion extending from a first end to an intermediate section of said second main body, and a second portion (13") extending from said intermediate section to said second end of said second main body; the second main body having also a lower surface adapted to be coupled to the bone and shaped on the anatomy of the patient's bone and thus following the negative of the surface of the bone; characterized in that said first portion of said second main body is superimposable on the second portion (2") of said first main body such that, the cutting instrument can follow the entire longitudinal opening, from the first end to the second end of the first main body, to perform the first part of the cut, wherein when the first part of the cut has been made, the first main body has been removed and the second main body has been fitted on the bone, there is a partial superimposition of the longitudinal opening of the second main body and the first part of the cut, and such that the second part of the cut can be made to complete the first part of the cut, by inserting the bone cutting instrument into the longitudinal opening of the second main body, from the first end to the second end. - at least a first main body having a longitudinal opening defining a cutting line for the insertion of a cutting instrument, extending from a first end to a second end of said first main body; said first main body has a first portion extending from said first end to an intermediate section, and a second portion (2") extending from said intermediate section to said second end; - at least two positioning and fixing arms (4a, 4b) extending away from said first main body from opposite sides with respect to said longitudinal opening, in order to correctly position said first main body on a bone and fix it thereto through respective fastening members; both the first main body and the positioning and fixing arms (4a, 4b) having a lower surface adapted to be coupled to the patient's bone, shaped on the anatomy of the patient's bone to enable the correct and univocal positioning thereof, such that the lower surface is the negative of the surface of the bone to which the first main body must be coupled; - a second main body having a longitudinal opening defining a cutting line for the insertion of a cutting instrument, extending from a first end to a second end of said second main body; said second main body having a first portion extending from a first end to an intermediate section of said second main body, and a second portion (13") extending from said intermediate section to said second end of said second main body; the second main body having also a lower surface adapted to be coupled to the bone and shaped on the anatomy of the patient's bone and thus following the negative of the surface of the bone; characterized in that said first portion of said second main body is superimposable on the second portion (2") of said first main body such that, the cutting instrument can follow the entire longitudinal opening, from the first end to the second end of the first main body, to perform the first part of the cut, wherein when the first part of the cut has been made, the first main body has been removed and the second main body has been fitted on the bone, there is a partial superimposition of the longitudinal opening of the second main body and the first part of the cut, and such that the second part of the cut can be made to complete the first part of the cut, by inserting the bone cutting instrument into the longitudinal opening of the second main body, from the first end to the second end.