The effect of various geometrical parameters of a grooved staggered herringbone micromixer on the mixing performance has been investigated using computational fluid dynamics. Mixing quality has been quantified with spatial data statistics, maximum striation thickness and residence time analyses. The results show that the number of grooves per mixing cycle does not affect the mixing quality in an important way. On the other hand, a larger groove depth and width allow the maximum striation thickness to be rapidly reduced, without increasing the pressure drop across the mixer. Wide grooves, however, create significant dead zones in the microchannel, whereas deep grooves improve the spatial mixing quality. (c) 2005 Elsevier Ltd. All rights reserved.