Abstract. In this work we provide a decomposition theorem for a class of quaternary signed-graphic matroids. The decomposition is based on [Formula: see text]-sums and a new operation called star composition, while the building blocks are graphic matroids and nongraphic matroids which become graphic upon the deletion of any cocircuit. This result generalizes previous results for binary signed-graphic matroids and graphic matroids, and it provides the theoretical basis for a recognition algorithm.