We present the results of the five mid-IR 15 mu m (12-18 mu m LW3 band) ISOCAM Guaranteed Time Extragalactic Surveys performed in the regions of the Lockman Hole and Marano Field. The roughly 1000 sources detected, 600 of which have a flux above the 80% completeness limit, guarantee a very high statistical significance for the integral and differential source counts from 0.1 mJy up to similar to 5 mJy. By adding the ISOCAM surveys of the HDF-North and South (plus flanking fields) and the lensing cluster A2390 at low fluxes and IRAS at high fluxes, we cover four decades in fur from 50 mu Jy to similar to 0.3 Jy. The slope of the differential counts is very steep (alpha = -3.0) in the flux range 0.4-4 mJy, hence much above the Euclidean expectation of alpha = -2.5. When compared with no-evolution models based on IRAS, our counts show a factor similar to 10 excess at 400 mu Jy, and a fast convergence, with alpha = -1.6 at lower fluxes.
