A method of producing a microstructured optical fiber, the method comprising providing a preform and drawing the preform , wherein the preform has a center axis, a length, a first end , and a second end and comprises a plurality of longitudinal holes extending lengthwise, and wherein the method comprises inserting a first end of a pressure tube into at least one of said holes of said preform at the first end of the preform and subjecting at least one of said holes of said preform to a controlled pressure via said pressure tube during the drawing, characterized in that the method comprises drawing the preform to the microstructured optical fiber in more drawing steps, wherein the more drawing steps comprises subjecting at least one of said holes of said preform to a controlled pressure via said pressure tube during the drawing, wherein the more drawing steps comprise a pre-drawing step that comprises subjecting at least one of said holes of said preform to the controlled pressure via said pressure tube during the drawing, and wherein the more drawing steps comprise a final-drawing step that comprises subjecting at least one of said holes of said preform to a controlled pressure via said pressure tube during the drawing, whereby the pre-drawing step provides that the relative diameter of at least one of said holes is increased by applying an increased pressure via the pressure tube to the at least one of said holes, such that the produced microstructured optical fiber has holes with different cross-sectional diameters. providing a preform and drawing the preform , wherein the preform has a center axis, a length, a first end , and a second end and comprises a plurality of longitudinal holes extending lengthwise, and wherein the method comprises inserting a first end of a pressure tube into at least one of said holes of said preform at the first end of the preform and subjecting at least one of said holes of said preform to a controlled pressure via said pressure tube during the drawing, characterized in that the method comprises drawing the preform to the microstructured optical fiber in more drawing steps, wherein the more drawing steps comprises subjecting at least one of said holes of said preform to a controlled pressure via said pressure tube during the drawing, wherein the more drawing steps comprise a pre-drawing step that comprises subjecting at least one of said holes of said preform to the controlled pressure via said pressure tube during the drawing, and wherein the more drawing steps comprise a final-drawing step that comprises subjecting at least one of said holes of said preform to a controlled pressure via said pressure tube during the drawing, whereby the pre-drawing step provides that the relative diameter of at least one of said holes is increased by applying an increased pressure via the pressure tube to the at least one of said holes, such that the produced microstructured optical fiber has holes with different cross-sectional diameters. wherein the more drawing steps comprise a pre-drawing step that comprises subjecting at least one of said holes of said preform to the controlled pressure via said pressure tube during the drawing, and wherein the more drawing steps comprise a final-drawing step that comprises subjecting at least one of said holes of said preform to a controlled pressure via said pressure tube during the drawing, whereby the pre-drawing step provides that the relative diameter of at least one of said holes is increased by applying an increased pressure via the pressure tube to the at least one of said holes, such that the produced microstructured optical fiber has holes with different cross-sectional diameters. <EOS>