Illex argentinus is known for spatiotemporally segregating into reproductive aggregations on the mid-continental shelf and slope off southern South America. In this study we found that the species also mates and spawns in San Matías Gulf, a coastal basin off northeastern Patagonia. Basing on the analysis of size and maturity structure of squids caught over a 28-month period in waters of the gulf, distinct demographic pulses were identified in the samples each year. Two of them were more consistent, one comprising small-sized individuals reaching full maturity in January to February (summer) and the other including larger individuals maturing between September and October/December (spring). Also, a less conspicuous group of mature individuals was observed in June/July (winter) of the last sampling year. So far, differences in the parameters of the size-at-maturity curves of these population components allow considering at least two stocks for management of I. argentinus in the gulf.