The microscope image of a thick fluorescent sample taken at a given focal plane is plagued by out of focus fluorescence and diffraction limited resolution. In this work, we show that Structured Illumination Microscopy (two or three beam SIM) data acquired in only one sample plane can be processed to provide an image with tight sectioning property and high transverse resolution. Our reconstruction algorithm is adapted from the blind-SIM technique which requires very little knowledge on the illumination patterns. It is thus able to deal with the possible illumination distortion induced by the sample. We named this new algorithm thick slice blind-SIM because it models a three-dimensional sample even though only a two-dimensional plane of focus was measured.