A deep marine seismic reflection profile was obtained across the Mesozoic rifted continental margin off Nova Scotia, eastern Canada. This profile crosses the Scotian Basin, one of the deepest basins on the margin of eastern North America, and it complements other deep crustal seismic data on this margin. The seismic data have been interpreted in conjunction with gravity anomaly and subsidence data. They show significant thinning of the continental crust over a zone about 200 km wide. The mode of extensional deformation is probably a combination of pure and simple shear; there is evidence for simple shear in the crust. The continent-ocean boundary lies near the seaward edge of synrift salt below the continental rise. A 100-km-wide zone of very thin (approximately 9 km or less) continental or transitional crust extends seaward from the outer shelf to this boundary. Reflectivity of the oceanic crust adjacent to the margin shows evidence of progressive igneous construction, perhaps modified by extensional faulting. This margin is nonvolcanic, and the transition to the volcanic margin off the eastern United States occurs about 500 km southwest of the seismic line. The width of the zone of crustal extension is much greater on this nonvolcanic margin segment than it is on the volcanic margin to the south. It seems likely that the prerift fabric of the continental lithosphere controls this width. A narrow rift may be prone to vigorous asthenospheric convection and therefore to more voluminous volcanism. However, significantly narrower zones of crustal extension occur on other nonvolcanic margins, so factors in addition to rift width, such as the rate of rifting, may also be important. ¿ American Geophysical Union 1995