THE SUGARCANE root system depth is crucial as it determines the potential depth of soil available for water and nutrient uptake by the crop. It was reported in an early publication that these roots could grow quite deep (6 m), but otherwise very little data are available on the root system depth. The present study was carried out in three countries: Côte d'Ivoire (var. NCo376), Brazil (var. RB72454) and Réunion, France (var. R570) at various sugarcane growth stages. There were no shoot or root growth constraints (deep soil with enough water). For plant cane, the root front growth (RF in cm) was linear. In Côte d'Ivoire, from 45 to 160 days after planting (DAP), RF = 0.81 DAP; R2 = 0.91. On the island of Réunion, from 100 to 280 DAP, sugarcane root front growth was: RF = 0.56 DAP; R2 = 0.70. When DAP was replaced by thermal time (TT: sum of degree-days), the root front growth patterns were quite similar in Réunion and Côte d'Ivoire (RF = 0.045 and 0.049 TT, respectively). In ratoon conditions, RF was stable when roots from the previous cycle were still in the soil at the onset of the cropping season. Thus, the observed root depth was approximately 4 m in Brazil and Réunion, even though the environment and cultivars were different. These findings showed that, when there is no marked crop growth constraint, roots of modern commercial sugarcane varieties can grow to depths of about 4 m in ratoon crops. While these values were lower than those reported in previous studies, they were higher than those generally accepted at present.