A concise assessment of the risks to human health and the environment posed by exposure to tributyltin oxide. This compound is an effective biocidal preservative for wood, cotton textiles, paper, and paints and stains for residential homes. Tributyltin oxide has also been added as an antifouling agent in numerous formulations of marine paints, from which it is slowly released to seawater. Tributyltin oxide is extremely hazardous to some aquatic organisms at very low concentrations. As a result, government restrictions have decreased the global use of tributyltin compounds in antifouling paints on small boats. The compound has been detected in water, sediment, and biota in areas close to pleasure boating activity, in treated fishnets, and in areas near cooling systems. Studies have reported bioconcentration in mollusks, fish, and in the liver and kidney of seabirds.