The Muon Portal Project has built a prototype of a real size detector (6m × 3m × 7 m) for the inspection of containers by muon tomography. This technique may provide 2D and 3D images of the interior of a container, to identify the presence of high- Z materials. In the present Project, 4800 extruded scintillator strips were arranged such as to cover four X-Y detection planes (6m × 3 m), two placed above and two below the container to be inspected. Silicon photomultipliers were used as photosensors, to collect the light transported by Wave Length Shifter (WLS) fibres embedded in the scintillator strips. First tomographic images are here presented.