The chemical composition of niaouli (Melaleuca quinquenervia) essential oils have been characterized by GC/MS and relative retention times. The leaf oil samples (144 samples obtained from leaves, collected during three seasons, on 48 different trees growing in Madagascar) were investigated for compound content, and 24 compounds were submitted to multivariate statistical analyses. Factorial discriminant analysis revealed the presence of four chemotypes: a chemotype having a high content of 1,8-cineole (37%); a chemotype relatively rich in 1,8-cineole (23%), viridiflorol (20%), and terpinolene (5%); a viridiflorol (48%) chemotype; and an (E)-nerolidol (87%) chemotype. The seasonal influence is negligible versus the chemical compound content of the chemotypes. The 1,8-cineole and (E)-nerolidol chemotypes represent 70% of the tree population.