A seismic-refraction profile was shot on the southern Grand Banks using large air-gun sources and an array of ocean-bottom seismograph receivers. A sediment column 1–2 km thick directly overlies Paleozoic basement with velocity structure similar to that of the Meguma Zone of Nova Scotia. The main crustal layer is 27 km thick, with seismic velocity of 6.3 km/s increasing to about 6.5 km/s in the lowest few kilometres. Complexity is apparent in the crust–mantle transition around 32 km depth. Comparison with deep multichannel reflection data suggests that the increased velocity in the lower part of the crust may be associated with a reflective zone and shows the Mohorovičić discontinuity to be delineated by a well-defined reflection. The absence of a major lower crustal layer of intermediate velocity (> 7 km/s) is consistent with observations elsewhere in the region.