An electrical interconnection system with high speed, differential electrical connectors. The connector is assembled from wafers containing columns of conductive elements, some of which form differential pairs. Each column may include ground conductors adjacent pairs of signal conductors. The ground conductors may be wider than the signal conductors, with ground conductors between adjacent pairs of signal conductors being wider than ground conductors positioned at an end of at least some of the columns. Each of the conductive elements may end in a mating contact portion positioned to engage a complementary contact element in a mating connector. The mating contact portions of the signal conductors in some of the pairs may be rotated relative to the columns. The printed circuit board to which the differential signal connector is mounted may be constructed with elongated antipads around pairs of signal conductors.