We describe the protocol for an objective quantification of cellular composition and fractional β-cell viability in pancreatic islet cell products. The method is based on the use of Laser Scanning Cytometry (LSC) and Fluorescence-Activated Cell Sorting (FACS) techniques performed on dissociated islet cells. Analysis of human islet preparations with these techniques allows for the definition of β-cell mass and viability, and could provide valuable potency assessment of human islets prior to transplantation. The need for analytical methods that are predictive of the quality and potency of cellular products has been recognized. Herein we describe the protocol for an objective quantification of cellular composition and fractional β-cell viability in pancreatic islet cell products. The method is based on the use of Laser Scanning Cytometry (LSC) and Fluorescence-Activated Cell Sorting (FACS) techniques performed on dissociated islet cells. Analysis of human islet preparations with these techniques allows for the definition of β-cell mass and viability, and could provide valuable potency assessment of human islets prior to transplantation.