Although studies of population genetic structure are commonplace, a strong bias exists towards species from low latitudes and with relatively poor dispersal capabilities. Consequently, we used 280 Amplified Fragment Length Polymorphism (AFLP) bands to explore patterns of genetic differentiation among eight populations of a high latitude broadcast-spawning marine mollusc, the Antarctic limpet Nacella concinna. Over three hundred individuals were sampled along a latitudinal gradient spanning the Antarctic Peninsula from Adelaide Island to King George Island (67º–62º S), then to Signy Island (60ºS) and South Georgia (54ºS). Populations from the Antarctic Peninsula exhibited little genetic structure, but were themselves strongly differentiated from both Signy and South Georgia. This finding was analytically highly robust and implies the presence of significant oceanographic barriers to gene flow in a species long regarded as a classic example of a widely-dispersing broadcast-spawner.