The photostability of polymeric systems can be extensively affected by the presence of dyes and pigments. Achromatic pigments such as carbon black are known as effective stabilizers for polymers, while pigments such as those based on metals oxides may accelerate photodegradation in polymers. Despite innumerous studies addressed to achromatic pigments, the effects and action mechanisms of chromatic pigments on polymer stability are not well established. In this work, an effective photostabilizer action on polycarbonate was verified by the incorporation of a red diazo type condensation pigment. This pigment was incorporated into polycarbonate in an extruder at a concentration of 1 wt %. Injection molded specimens of this material were submitted to photochemical aging following the recommendations of ASTM G-53. The nonaged and aged specimens were characterized by mechanical testing, infrared spectroscopy, UV/visible absorption and fluorescence spectroscopies, and electron spin resonance. The absorption of the UV radiation by the pigment and subsequent quenching by the internal conversion energy process is the probable stabilization mechanism involved in this polymeric system. (C) 2007 Wiley Periodicals, Inc.