The Gulf sturgeon (Acipenser oxyrinchus desotoi) was listed as a threatened species in 1991 because of declines in abundance throughout the Gulf of Mexico. One recommendation of the recovery plan for Gulf sturgeon was to characterize critical habitats. In this study, radio telemetry was used to determine summer (June-August) distribution and habitat use of Gulf sturgeon in the Choctawhatchee River, Florida-Alabama. Ranging from 74 to 222 cm total length, 63 radio-tagged fish were located 398 times during weekly or biweekly searches in June-August of 1994-1997. A 10-km section of the lower Choctawhatchee River (river km 40-49.9) accounted for 38% of the summer locations of immature fish (less than 1.3 m fork length) and 73% for mature fish. Fish were typically located at sites that were 2-5 m in depth, with water temperatures of 25-28??C and a sand substrate. Spring discharges account for up to one-third of the mainstem river flow in this reach, but water temperatures at fish locations were similar to temperatures at fish locations in all other sections of the river. Efforts to monitor and improve habitat quality should be focussed on this river reach, given that a high percentage of the total Choctawhatchee River population occurs there during summer.