After the encounter with the Giotto spacecraft, the comet P/Grigg-Skjellerup was observed with the 2.2 m ESO telescope. Imaging in the V and R bands and infrared photometry with the J and H filters were performed. From the radial enhancement of the images we derived that the R frame mainly concerns the dust tail of the comet. Thus we applied the inverse numerical method of dust tail analysis in order to estimate the following cometary-grain parameters: ejection velocity, anisotropy of the emission, size distribution and loss rate. This from the observations back in time to the Giotto encounter. From infrared observation we could calculate the J and H magnitudes and the colour index J-H=0.4 consistent with previous measurements of the comet. © 1993 Societàa Italiana di Fisica.