This work investigates drop-size distribution measurements with a laser diffraction technique of sprays produced by a pintle type, outward-opening injector driven by a piezo-actuator at injection pressures up to 20 MPa. Considering the high injection pressures, multiple scattering effects are expected. The multiple scattering effects were first verified and it is found that these effects are negligible when the transmission is greater than 13%. This limit is far less than the one found by many works of the literature that reported a limit in transmission of the order of 40%. One of the reasons for this difference is believed to be due to the specific characteristic features of the present spray drop-size distributions. A procedure based on the correction of the light intensity collected by each diode has been developed to get rid of the undesirable multiple scattering effects. This procedure, which returns analytical correction factors as a function of the transmission, allows reliable drop-size distribution to be obtained for injection pressure up to 20 MPa. Among other results, it is found that the piezo injector produces bi-modal spray drop-size distributions at high injection pressure. Finally, these distributions are successfully modelized by the application of the MEF. According to the injection pressure, the mathematical drop-size distributions are functions of three or five parameters whose correlations with the injection pressure have been derived.