Numerical simulations of light scattering by a biconcave shaped human red blood cell (RBC) are carried out using the finite-difference time-domain (FDTD) method. A previously developed FDTD code for the study of light scattering by ice crystals is modified for the current purpose and it is validated against Mie theory using a spherically shaped RBC. Numerical results for the angular distributions of the Mueller scattering matrix elements of an RBC and their dependence on shape, orientation, and wavelength are presented. Also calculated are the scattering and absorption efficiencies. The implication of these results on the possibility of probing RBC shape changes is discussed. © 2005 Society of Photo-Optical Instrumentation Engineers.