Ocean general circulation models frequently use nonuniform grids, especially in the vertical direction. This paper clarifies the implications of using such grids on the consistency and accuracy of numerical schemes. It is emphasized that numerical schemes maintain their order of accuracy on a nonuniform grid provided the grid can be related to a smooth mapping. Additional metric terms appear in the truncation error, which should not be interpreted simply as a numerical diffusion. ¿ American Geophysical Union 1996