The growth of Octopus vulgaris (Mollusca: Cephalopoda) in tanks and the sea was modelled and calculated following tagging studies in Senegal. Octopus exhibits a large individual variability in growth and the exponential growth curve is the best fitting theoretical model among other usual models tested. Globally, the growth rates were comparable in the sea and in tanks. Growth rates for the hot season were lower than those for the cold season. Applied to in situ data, the statistical tests showed that females grow more quickly than males. Life expectancy was estimated at between 12 and 14 months. These results question the previous growth curves for the region, all of which were obtained from modal analysis using size or weight–frequencies and were used during stock assessments of this important resource off the north-west African coast.