The European sturgeon (Acipenser sturio) is a diadromous species that spawns in the rivers in late spring and early summer. The juveniles then spend around two years in the brackish waters (5 to 25 PSU) of the estuary zone before moving out to sea. This study describes the downstream migration evolution from October 1994 to August 1996 of juvenile sturgeon, born in the Gironde basin in the summer of 1994. For the purposes of the study, the inland section of the Gironde estuary was sampled by trawl monthly. The trawls - average duration 32 minutes, average length approx. 4 200 m - were conducted according to a sampling plan, stratified into 13 major zones from the oligohaline (0.5 to 5 PSU) to the polyhaline sectors (18 to 30 PSU) of the estuary. The study shows that the first members of the 1994 cohort (TL=27 cm) were caught in early March 1995 in the zones furthest upstream. A distinction appears between an initial period, in which the fish live mainly in the upstream zones of the marine estuary, and a second, starting from their second growth period (April 1996), in which the juveniles are split into two separate areas about twenty kilometres apart. The two zones are situated 18 km and 38 km respectively from the mouth of the estuary and they do not appear to be any different to their neighbours as regards to depth and type of bed. There is no significant biometric difference (length, weight) between the juveniles of the two zones. However, individual marking has helped to highlight exchanges of animals between the two sectors. The study shows that, within this large estuary of relatively homogeneous depth (4 to 10 m) and type of substrate (sand/mud, gravel), the juveniles inhabited two quite distinct zones in 1996 before they left the estuary for the sea.