Cell-centered and vertex-centered multigrid methods for solving interface problems are studied. These methods differ in the location of the nodes in the grids and in the transfer operators. It is shown how by means of stencil notation a compact and precise description can be given of the transfer and coarse grid operators. A structured FORTRAN description of the fundamental multigrid algorithm with only one goto statement is presented. Numerical results of several test problems with strong discontinuities in equation coefficients are presented. Storage and work requirements are discussed.