A theoretical study of the AlC3 species has been carried out. There are three species that lie quite close in energy: a rhombic four-membered ring, 1((2)A(1)), a T-shape structure, 2(B-2(2)), and a linear species, 3((II)-I-2). The linear isomer is predicted to be lower in energy, but 1((2)A(1)) lies only about 1-2 kcal mol(-1) higher. In any case, it seems that both isomers could be accesible to experimental detection. Our conclusion is in contrast with a previous theoretical study on this system that predicted a quartet state as the global minimum.