A steerable instrument for endoscopic and/or invasive type of applications, such as in surgery, the instrument comprising an elongated tubular body having at least one actuation zone (14; 15) at a proximal side of the steerable instrument and at least one bendable zone (16; 17) at a distal side of the steerable instrument, said at least one actuation zone (14; 15) being arranged to control bending of said at least one bendable zone (16; 17) by means of a plurality of longitudinal elements, the steerable instrument having a cylindrical diameter adaptation section extending a distance in a longitudinal direction of the elongated tubular body over which the longitudinal elements change from a first distance from an axis of symmetry at a first side to a second distance from said axis of symmetry at a second side, wherein the longitudinal elements comprise at least a first set of at least one longitudinal element and a second set of at least one longitudinal element, said at least one longitudinal element of the first set is part of a first intermediate cylindrical element and is located at said first distance from said axis of symmetry at said first side as well as within said cylindrical diameter adaptation section, the first intermediate cylindrical element having a first radius equal to said first distance, said at least one longitudinal element of the second set is part of a second intermediate cylindrical element and is located at said second distance from said axis of symmetry at said second side as well as within said cylindrical diameter adaptation section, said first distance being different from said second distance, the second intermediate cylindrical element having a second radius equal to said second distance, each one of said at least one longitudinal element of the first set overlapping with one of said at least one longitudinal element of the second set within said cylindrical diameter adaptation section as seen in a radial direction from said axis of symmetry, and being at least one of connected and attached to said one of said at least one longitudinal element of the second set, such that a movement of said one of said at least one longitudinal element of the first set in a longitudinal direction of said steerable instrument results in a same movement of said one of said at least one longitudinal element of the second set in said longitudinal direction to thereby control bending of said at least one bendable zone (16; 17) the longitudinal elements comprise at least a first set of at least one longitudinal element and a second set of at least one longitudinal element, said at least one longitudinal element of the first set is part of a first intermediate cylindrical element and is located at said first distance from said axis of symmetry at said first side as well as within said cylindrical diameter adaptation section, the first intermediate cylindrical element having a first radius equal to said first distance, said at least one longitudinal element of the second set is part of a second intermediate cylindrical element and is located at said second distance from said axis of symmetry at said second side as well as within said cylindrical diameter adaptation section, said first distance being different from said second distance, the second intermediate cylindrical element having a second radius equal to said second distance, each one of said at least one longitudinal element of the first set overlapping with one of said at least one longitudinal element of the second set within said cylindrical diameter adaptation section as seen in a radial direction from said axis of symmetry, and being at least one of connected and attached to said one of said at least one longitudinal element of the second set, such that a movement of said one of said at least one longitudinal element of the first set in a longitudinal direction of said steerable instrument results in a same movement of said one of said at least one longitudinal element of the second set in said longitudinal direction to thereby control bending of said at least one bendable zone (16; 17)