The presence of bromide can lead to the formation of brominated disinfection by-products (DBPs) upon ozonation. This study looked into the formation of brominated DBPs from natural waters containing the bromide ion. Ozonation of waters containing bromide ion produces both organic and inorganic by-products. Formation of by-products is a function of bromide ion concentration, the source and concentration of organic precursors, pH, ozone dose, temperature, DOC, alkalinity and reaction time; the effect of each of these parameters are discussed. Formation of organic by-products is favored at low pH whereas formation of bromate is favored at high pH. An increase in bromide ion concentration resulted in increased amounts of by-products and total organic bromine (TOBr). Control of by-products can be effected by using PEROXONE (hydrogen peroxide plus ozone) or ammonia. PEROXONE produced 55% less organic by-products at the cost of a 25% increase in bromate. Ammonia addition resulted in a 30% decrease of both organic and inorganic by-products.