This paper reports an experimental investigation on the practical use of a laser-diffraction instrument, the Malvern Spraytec 2007, to characterize highly transient sprays produced by a high-pressure GDI injector. The sprays are large, composed of very small drops, dense and heterogeneously distributed in space. These characteristics may be at the origin of undesirable effects (beam steering, vignetting and multiple light scattering) that bias the measurements. The manifestation of these effects is experimentally identified and solutions to erase their influence are provided. A particular attention is paid on the multiple light scattering effects. A correction procedure is developed. It consists in determining a correction factor series to be applied on the normalized light intensity distribution. The corrected dropsize distributions are calculated from the new light intensity distribution. Furthermore, this procedure succeeds in correcting vignetting effects. Despite the correction procedure is applicable for the present operating conditions only, this work defines a clear protocol to apprehend laser-diffraction spray characterization in severe operating conditions and to establish a correction procedure if required. Among other results, it is emphasized that the combination of the Spraytec and the correction procedure performances allows the temporal evolution of the drop-size distribution during an injection and cycle-to-cycle spray drop-size distribution variations to be determined. Such information is of paramount importance and the Spraytec is probably the sole instrument able to provide it.