The Smagorinsky subgrid model is revised to properly account for grid anisotropy, using energy equilibrium considerations in isotropic turbulence. For moderate resolution anisotropies, Deardorff’s estimate involving an equivalent grid scale &Dgr;eq=(&Dgr;1&Dgr;2&Dgr;3)1/3is given a rigorous basis. For more general grid anisotropies, the Smagorinsky eddy viscosity is recast as &ngr;T=[cs&Dgr;eqf(a1,a2)]2‖S˜‖, wheref(a1,a2) is a function of the grid aspect ratiosa1anda2, and ‖S˜‖ is the resolved strain rate magnitude. The asymptotic behavior of &ngr;Tat several limits of the aspect ratios are examined. Approximation formulas are developed so thatf(a1,a2) can easily be evaluated in practice, for arbitrary values ofa1anda2. It is argued that these results should be used in conjunction with the dynamic model of Germanoetal. whenever the anisotropy of the test‐filter differs significantly from that of the basic grid.