One of the few remaining fisheries for Atlantic sturgeonAcipenser oxyrinchustakes place during spring and fall in the New York Bight, but no information on the stock composition of this fishery is available. We used data from mitochondrial DNA (mtDNA) restriction fragment length polymorphism analysis to estimate the relative contributions of source stocks of Atlantic sturgeon to a New York Bight fishery sample (N= 112) collected in 1993 and 1994. Composite mtDNA haplotype frequencies of source populations were first characterized with five informative restriction enzymes:BglI,MspI,EcoR V,Hinf I, andHincII. All St. Lawrence River, Quebec, and St. John River, New Brunswick, specimens had an identical haplotype (genotypic diversity = 0.0); for the purposes of mixed-stock analysis, both populations were pooled as the “Canadian stock.” Genotypic diversity ranged between 0.483 and 0.750 among samples from the Hudson River in New York, the Edisto River in South Carolina, and the Ogeechee, Altamaha, and Satilla rivers in Georgia. Chi-square analyses indicated that the Edisto, Savannah (Georgia), Ogeechee, Altamaha, and Satilla River samples should be grouped as the “southeastern stock,” and that haplotype frequencies of the three source stocks (Canadian, Hudson River, southeastern) were highly heterogeneous (P= 0.0000). Mixed-stock analysis with a constrained least-squares approach under the conditional method indicated a 97.2% Hudson River contribution, a 2.8% contribution by the southeastern stock, and a 0.0% contribution by the Canadian stock; the unconditional method provided estimates of 99.1%, 0.9%, and 0.0%, respectively. Frequencies of mtDNA haplotypes of subadults (N= 30) from a seasonal aggregation of Atlantic sturgeon from the lower Delaware River were intermediate between those of the Hudson River and southeastern stocks. This finding, together with ancillary information, suggests that the Delaware River aggregation is primarily either a mixture of both the Hudson River and southeastern stocks or of the Hudson River stock and a relict Delaware River stock.