As part of a study of growth ring structure and growth periodicity in tropical trees, the formation of indistinct growth rings in young Hevea brasiliensis cultivated in Peninsular Malaysia was investigated. The cycle of shoot elongation included the following stages: apical growth (three phases), leaf maturation (two phases), and radial growth with no change in appearance (one phase). Correlation analysis of height and radial increment revealed a 6-week cycle and a 4- to 5-week delay between the height increment and the radial increment. The darker bands visible on wood disks had radially flattened wood fibres and characteristic vessels in radial multiples. It is suggested that the darker bands include growth ring boundaries, but with quite different radial variation of fibre thickness than in growth ring boundaries of temperate trees.