Polycyclic aromatic hydrocarbons (PAHs) are a class of planar molecules that can induce chemical carcinogenesis. Their carcinogenic powers vary in a large range, from the very strong carcinogens to the inactive ones. Many models have been proposed to explain the PAHs' carcinogenic activity, but all of them present some failures. Here we introduce a new methodology to identify PAHs' carcinogenic activity based on the concept of electronic local density of states (LDOS). We show that the analysis of the molecular energy levels in association with the LDOS calculated over the ring which contains the highest bond order of the molecule allows simple rules to identify whether a specific PAH molecule will present (or not) carcinogenic activity.77611861189