To determine the present and future role of tropical tree plantations in the global carbon budget, data on rates of plantation establishment and their commercial volumes, by species groups and age-classes, were gathered and converted to biomass and ultimately to carbon fluxes. The rate of plantation establishment has increased dramatically since the 1940's, resulting in an area in 1980 of about 11 × 106 ha with more than 60% of this area planted during the last decade. Total biomass of plantations is estimated to range from 0.65 × 109 to 2.22 × 109 t or about 1% of the biomass of natural forests. Most of the biomass (79%) is in the 6- to 30-year-old plantations. We estimate that tropical plantations are a small sink of atmospheric carbon of 0.03–0.11 × 109 t C/year, most of which occurs in the two youngest age-classes. Although this flux is small, it may be sufficient to balance the small source of carbon from harvesting forests and other land-use changes in the temperate zone.