A study was made on the development and distribution of the root system of tomato plant (Lycopersicon esculentum Mill.), var. Santa Cruz IAC-2731, at 25, 50 and 75 days after transplanting in a reddish-yellow latossol, "fase argilosa, série Barão - Campinas", State of São Paulo. About sixty three percent of roots were found in the upper 10 cm layer of the soil, at the three ages considered. The root system of plants was already fully development at the 25th day when reached a depth of 1.30 m; it reached 1.90 m by 50 days and 2.50 m by 75 days. It is suggested that application of fertilizers and irrigation might be confined to the upper 10 cm layer of the soil for the best utilization by tomato plants.