Wall-slip effects in a rheometer with double concentric cylinder geometry may lead to significant errors in measurement of the apparent viscosity. Previously, we proposed to use a slotted rotor design to reduce these effects. In this paper, we conduct two as well as three-dimensional computational fluid dynamics (CFD) simulations to determine the differences in rheological measurements of yield stress fluids between the slotted and non-slotted rotor designs. The test fluid and the slip wall boundary of a rotor are characterized in our computational model by the constitutive equation of Zhu et al. ["Non-Newtonian fluids with a yield stress," J. Non-Newtonian Fluid Mech. 129, 177-181 (2005)] and the wall-slip length method, respectively. The model has been validated against the existing rheological data measured using a vane rheometer. The results of this study indicate that the rheometer equipped with a slotted rotor can measure the fluid properties with enhanced accuracy and less sensitivity to the wall-slip velocity than a rheometer with a non-slotted rotor. We also show that the wall-slip effects can be further reduced by either increasing the slot ratio or adding more slots to the rotor. This work illustrates that CFD analysis can be a powerful tool in rheometer design. (C) 2010 The Society of Rheology. [DOI: 10.1122/1.3484955]