On the basis of first-principles electronic band structure theory, we calculated the refractive indices of the zinc blende and wurtzite structures of the chalcogenides ZnQ and CdQ (Q = O, S, Se, Te) and analyzed their trends by calculating the total absorption power per unit formula. The calculated refractive indices are in good agreement with the available experimental data. The total absorption power per formula unit is found to allow one to distinguish the effect of the chromophore from that of the cell volume on the refractive indices of insulating inorganic compounds.