Many long linear troughs are visible in synthetic aperture radar images of the surface of Venus. Their geometry closely resembles that of dike swarms on Earth. Such troughs will be formed if dikes fail to reach the surface, or if the magma in them is partially drained. Dikes that form closed ellipses in plan view can be produced by intrusions near a depression, and intersecting dikes can result if the stress field changes with time. Because of the absence of erosion and sedimentation, all these effects are better displayed on Venus than they are on Earth. The magnitude of the regional stress on Venus can be estimated from the dike patterns to be about 3 MPa, or similar to that of Earth. Dikes consisting of en echelon segments whose total length is 1500 km or more occur on both Earth and Venus. On Earth their widths are generally greater than 30 m and are sometimes as great as 250 m, and they are likely to be similar on Venus. The melt velocity during their emplacement is predicted to be a few meters per second, and the calculated rate of heat loss is sufficiently slow that they can remain molten as they propagate for distances of more than 1000 km. The same calculations apply to sills, though less is known about their geometry. The results therefore suggest that magma intrusion in thin sheets extending over 1000 km or more could produce regional crustal thickening and uplift on both Earth and Venus.