Three-dimensional (3D) isotropically sampled data facilitates retrospective viewing of arbitrarily aligned image planes and simplifies automated computer analysis of 3D structures. However, compared to acquisitions that employ thick slices, MRI acquisitions with isotropic sampling have a lower signal-to-noise ratio (SNR). A rater study was performed to examine viewer preference for the trade-off between SNR and the partial-volume effect of through-plane averaging. A robust preference for a 5:1 ratio in through-plane to in-plane was found for a typical SNR of 11. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc.