We have found that vinculin is localized at the sarcolemma of skeletal muscle cells in a two-dimensional orthogonal lattice. Perpendicular to the longitudinal axis of the cell, bands of vinculin encircle the muscle cell and repeat along its length with a periodicity corresponding to the subjacent sarcomeres. Because of their appearance and probable function, we call the transverse elements of the lattice "costameres" (Latin costa, rib; Greek meros, part). Costameres have a substructure consisting of densely clustered patches of vinculin; the patches are segregated into two rows which flank the Z line and overlie the I band of the underlying sarcomere. It is likely that the costameres are physically coupled to the underlying myofibrils because: (i) the costameres broaden and narrow in concert with the underlying I band in stretched and contracted muscle, and (ii) adjacent but misaligned myofibrils are mirrored by corresponding discontinuities in the overlying costameres. We hypothesize that the sarcolemmal lattice, detected because vinculin is one of its molecular components, integrates the contractile apparatus with the sarcolemma during lengthening and shortening of the muscle cells.