Density functional theory has been used to investigate the structure, stability and aromaticity of a series of nitrogen-containing oxocarbons, which are related to CnOn2- (n = 3-6). We have identified a large number of minimum-energy species which might be synthesized and calculated their aromaticity using the nucleus-independent chemical shift method of Schleyer. Successive substitution of carbon by nitrogen reduces their stability, as reflected in the calculated bond orders and dissociation energies. In general, there is no close correlation between the stability and pi -aromaticity of the species studied.