Grasses exhibit a large genetic variability in leaf growth and length, with major consequences on productivity and morphology of forage/turf types. The cellular components of the variability in leaf growth were analysed in Lolium perenne L., on eight genotypes of contrasting leaf length from a forage type mapping population, and on one turf genotype. Leaf elongation rate, cell number and size, and cellular dynamics in the leaf growth zone were determined on leaf 6. The variability in mature leaf length was due to variability in rate rather than duration of leaf elongation. In the forage type population, variability in leaf growth rate was due to variation in cell production rate and to variation in the number of cells simultaneously elongating in the growth zone, whereas elongation rate and duration of individual cells were similar. In the turf type, the lower leaf elongation rate was due to a decrease in both cell production and cell elongation rates. In conclusion, cell division plays a major role in genetic variation of leaf elongation among forage types, but cell elongation rate also discriminates between turf and forage types.