Two molecular methods, mitochondrial DNA and introns, were used to determine genetic relationships among Antarctic toothfish, Dissostichus mawsoni, samples from three CCAMLR areas 48.1, 88.1, and 58.4.2. D. mawsoni appeared to be characterized by low diversity; no genetic variation was detected with restriction enzyme digests of nine sub regions of the mitochondrial genome. Polymorphisms were found in four out of seven introns digested with the restriction enzymes, but there was no population differentiation among the three sea areas. While direct sequencing of cytochrome b (665 base pair) showed virtually no variation, sequences for ~600 bp of the left domain of the control region showed nucleotide variation with some haplotypes restricted to sea areas. The weak genetic differentiation is supported by oceanic gyres, which may act as juvenile retention systems, and by limited movement of adult tagged fish. It is recommended that the Ross Sea D. mawsoni be treated as a separate stock unit.