An experimental investigation was performed on a NACA 0012 airfoil with three-dimensional and two-dimensional leading-edge glaze ice accretions. The study was performed to provide a better understanding of the relation between the iced-induced flowfield and the airfoil performance. The upper-surface rms pressure coefficient achieved a maximum value that increased with increasing airfoil incidence and occurred at a location that moved downstream with increasing angle of attack. This trend continued until maximum mean lift was attained, after which the maximum rms pressure occurred at a constant location. Time-dependent surface pressure measurements indicated the movement of increased suction pressure over the airfoil surface at a convection velocity equal to half the freestream velocity. This may represent the motion of vortices in the separated shear layer. Elevated rms lift and moment coefficients were also observed prior to the maximum mean values. Comparison of the three-dimensional and two-dimensional ice shapes revealed a shorter length separation bubble aft of the three-dimensional shape that led to a slightly higher maximum lift. This resulted from the formation of additional vortices in the separated shear layer due to the jaggedness of the three-dimensional ice shape. The vortices acted to enhance mixing in the shear layer causing early reattachment.