A linear retention index system for temperature-programmed capillary gas chromatography of polycyclic aromatic compounds using naphthalene, phenanthrene, chrysene, and picene as internal standards has been used in this laboratory for routine analysis since 1979. Conclusions from a data set of 29 routine capillary gas chromatographic analyses of a complex mixture of polycyclic aromatic compounds are used to evaluate, describe, and justify the polycyclic aromatic compound retention index system. The number, width, and linearity of the interpolation intervals are described. The effects on the retention indices of variations in programming rate, column internal diameter, and initial temperature are discussed. The polycyclic aromatic compound retention index system is shown to be a consistent, useful tool for preliminary identification of polycyclic aromatic compounds in complex mixtures. Tables listing standard retention indices for polycyclic aromatic hydrocarbons, polycyclic aromatic sulfur heterocycles, and nitrogen-containing polycyclic aromatic compounds are included.