A microstructured multicore optical fibre suitable for being manufactured with a stack-and-draw method, having a cladding (4.1) containing a microstructured area with longitudinal areas (3.1) and a plurality of cores (2.1) fabricated of glass, especially of doped silica glass, or of polymer wherein a refractive index of the cladding (4.1) is greater than refractive index of the longitudinal areas (3.1), the cores (2.1) are located at nodes of a hexagonal lattice with a lattice constant Λ in a matrix of glass, and are separated one from another with the longitudinal areas (3.1) arranged between them, the longitudinal areas (3.1) are distributed on vertices and middle points of sides of hexagons, centres of said hexagons are designated by particular cores (2.1) and the sides of said hexagons have a length defined by centres of the longitudinal areas (3.1) located on the vertices of said hexagon the lengths of said sides are equal to double the lattice constant 2Λ, wherein the centers of adjacent longitudinal areas are spaced by the lattice constant Λ, characterized in that an area between the core (2.1) and the longitudinal areas (3.1) separating core (2.1) from the other cores, constitutes an internal cladding surrounding said core (2.1) so that a difference of refractive index between the core and both the cladding (4.1) and the internal cladding is in the range Δ=5.63·10 -3 ±2.9·10 -3 at a wavelength of 1550 nm, and at least one core (2.1) is surrounded by 12 longitudinal areas (3.1) having centres located on vertices and middle points of sides of a hexagon, the centre of which is designated by said core (2.1), and a distance between adjacent cores b is equal to either b = 2 ⋅ Λ ⋅ 3 or b = 4 ⋅ Λ , so as to provide single-mode operation at 1550 nm. a stack-and-draw method, having a cladding (4.1) containing a microstructured area with longitudinal areas (3.1) and a plurality of cores (2.1) fabricated of glass, especially of doped silica glass, or of polymer wherein a refractive index of the cladding (4.1) is greater than refractive index of the longitudinal areas (3.1), the cores (2.1) are located at nodes of a hexagonal lattice with a lattice constant Λ in a matrix of glass, and are separated one from another with the longitudinal areas (3.1) arranged between them, the longitudinal areas (3.1) are distributed on vertices and middle points of sides of hexagons, centres of said hexagons are designated by particular cores (2.1) and the sides of said hexagons have a length defined by centres of the longitudinal areas (3.1) located on the vertices of said hexagon the lengths of said sides are equal to double the lattice constant 2Λ, wherein the centers of adjacent longitudinal areas are spaced by the lattice constant Λ, characterized in that an area between the core (2.1) and the longitudinal areas (3.1) separating core (2.1) from the other cores, constitutes an internal cladding surrounding said core (2.1) so that a difference of refractive index between the core and both the cladding (4.1) and the internal cladding is in the range Δ=5.63·10 -3 ±2.9·10 -3 at a wavelength of 1550 nm, and at least one core (2.1) is surrounded by 12 longitudinal areas (3.1) having centres located on vertices and middle points of sides of a hexagon, the centre of which is designated by said core (2.1), and a distance between adjacent cores b is equal to either b = 2 ⋅ Λ ⋅ 3 or b = 4 ⋅ Λ , so as to provide single-mode operation at 1550 nm. <EOS>