Summer flounderParalichthys dentatuswere collected from intertidal and subtidal polyhaline marsh creeks in the Great Bay–Little Egg Harbor estuarine system in southern New Jersey during 1987–1990 to determine seasonality, duration of creek use by individuals, emigration rate, foraging habits, and daily growth rate of young-of-year fish in those habitats. Four hundred fifty-eight age-0 individuals (mean total length [TL], 238 mm; range, 156–312 mm) were collected from a combination of weir, seine, gill-net, and gig sampling. They were available to the collecting gear from late July through October, peaking numerically in September. Sixty-three (39%) of 162 tagged age-0 summer flounder were recaptured at least once during August–September. The average period of creek use was estimated at 17 d (range, 5–38 d) from release. Decline in percent recaptures suggested an emigration rate of 1.0%/d and 100% emigration within 50 d of release during August–October. Summer flounder appear to undergo tidal movements in and out of the creeks. Average growth rate predicted by length-frequency analysis was 1.7 mm/d, whereas growth rate measured directly from tag recaptures averaged 1.3 mm/d. Summer flounder preyed on creek fauna in order of prey abundance; Atlantic silversidesMenidia menidia, mummichogsFundulus heteroclitus, marsh grass shrimpPalaemonetes vulgaris, and sevenspine bay shrimpCrangon septemspinosacontributed most importantly to their diets. Stomach fullness of fish captured leaving the creeks on ebb tides was significantly greater than that of fish captured entering the creeks on flood tides, suggesting that summer flounder undergo tidal movements to take advantage of high concentrations of prey available in the creeks. These analyses provide compelling evidence that salt-marsh creeks in southern New Jersey are important nursery habitats for young-of-year summer flounder.