The present invention relates to fire retardant polymer composition obtained by the incorporation of N-tribromophenylma­leimide as a fire retardant additive. The preferred amount of bromine is above 0.5% by weight of the composition. The polymer is selected from polystyrene, styrenic polymers and copolymers, rubbers, epoxy resins, plasticized PVC, polyurethanes and ABS resins. If desired, one or more additional fire retardant may be incorporated in the composition. Optionally synergistic fire retardant additives such as antimony oxide, or organo-phosphorus compounds are also incorporated. The flame retardant polymer compositions have improved properties compared with those obtained with known flame retardant reagents. It was also unexpectedly found that the fire retardant additive imparts stability against ultraviolet light irradiation to the polymer composition.