The fabrication of lines at the surface of polymethyl-methacrylate (PMMA) was studied. A femtosecond laser with pulse duration of 450 fs and wavelength of 1027 nm was used. The z-scan method was employed as a focusing procedure to control the sample position with respect to the beam waist through transmittance measurements. This allowed the production of continuous lines with a length of 2 mm on the surface of the PMMA sample. The variation of the lines profiles and dimensions was studied for different values of the sample position with reference to the beam waist. Also effects on the lines fabricated at different values of incident energy and separation on the sample surface between consecutive impinging laser pulses were investigated. A range of positions where lines with similar features and sizes were produced was obtained. Submicrometric surface modifications were achieved as surface swelling in form of successive bumps. After inspecting the sample cross section, it was observed that depending on the relative position of the beam waist regarding the sample surface, inner modifications appear under the modified material surface. (C) 2014 Elsevier B.V. All rights reserved.