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Maturity classification is an important concept to provide the best allocation of resources for soybean [Glycine max (L.) Merr.] research and commercialization. A similar maturity group system used in North America is being used for some seed companies in Brazil and needs research to improve its use. This study evaluated the maturity stability of 48 midwestern and 40 southern Brazilian commercial cultivars ranging from North American maturity groups VI to VIII at 15 locations. Relative maturity groups were attributed to all cultivars. All trials were planted in the first half of November. The effect of location was very important in influencing the number of days to maturity, number of days to flowering and reproductive growth period (RGP). The genotype x environment interaction, although statistically significant, was much lower than the individual effects of environment and genotype for all traits and regions. Genotype x latitude and genotype x altitude, considering also years of evaluation, were generally low or nonsignificant. A recommended list was developed of the most stable genotypes and, consequently, of the most suitable check genotypes for each maturity group classification in the southern and midwestern regions. Results indicate that the use in Brazil of a maturity group system similar to that used in North America to classify soybean genotypes is an efficient method for describing relative maturity on a broad environmental basis.