A printed circuit board transmission line has an outer conductive wall surrounding an inner dielectric core. The transmission line may be disposed inside a grounded shielding to provide a form of coaxial conductor that mitigates cross talk from adjacent transmission lines and EMI. Further, groups of dielectric-core transmission lines may be disposed within a single grounded shield. For example, edge coupled differential pairs may be disposed in parallel with each other on a plane defined by a layer of the printed circuit board, i.e., side-by-side. Further, broadside-coupled differential pairs of dielectric-core transmission lines may be disposed in parallel with each other in a stack which is orthogonal with the plane defined by a layer of the printed circuit board, i.e., one on top of the other. Further, a plurality of dielectric-core transmission lines which may include all or ones of single-ended lines and differential pairs may be disposed within a single grounded shield.