Whereas commercially available hematological analyzers measure volume of individual platelets, angle-resolved light-scattering provides unique ability to additionally measure their shape index. We utilized the scanning flow cytometer to measure light-scattering profiles (LSPs) of individual platelets taken from 16 healthy donors and the solution of the inverse light-scattering problem to retrieve the volume and shape index of each platelet. In normal conditions, the platelet shape index distribution (PSID) demonstrates three peaks, which relate to resting, partially activated, and fully activated platelets. We developed an algorithm, based on fitting PSID by a sum of three peak functions, to determine the percentage, mean platelet shape index, and distribution width of each platelet fraction. In total, this method gives eight additional parameters of platelet morphology and function to be used in clinical hematological analysis. We also stimulated the platelets with adenosine diphosphate (ADP) and measured the dependence of equilibrium PSID, including the total percentage of activated platelets, on ADP concentration.