Gravity data from mid-ocean ridges are routinely used to infer crustal thickness variations. Commonly, the contribution to the gravity anomaly from mantle density variations are taken into account, but variations in crustal density are rarely considered. Wide-angle seismic experiments conducted in the same locations as detailed gravity surveys on the mid-Atlantic Ridge show that the crustal thickness inferred from gravity data can deviate substantially from that derived from seismic data, particularly in the vicinity of ridge offsets. This discrepancy may be partly attributed to unmodeled crustal density variations: at slow-spreading ridges, crust formed near ridge offsets has consistently lower velocity than crust formed near segment centers, and a corresponding density reduction of up to 20% may be inferred. ¿ American Geophysical Union 1996