Ground deformation around the CANNIKIN underground nuclear explosion was studied by means of geodetic measurements, observation of tilt in lakes, and analysis of high-speed motion pictures. The lengths of 53 lines of the order of 1 km long located as many as 7 km from ground zero (GZ) were measured before and after the explosion. Principal strains calculated from the observed changes in length indicate northeast-oriented extension, which is interpreted as reflecting, in part, the release of tectonic strain. Information from an incomplete remeasurement of level lines indicates as much as about 1 m of residual uplift along nearly 2 km of the Bering coast adjacent to the explosion site. Measurements of tilt at six lakes differ in magnitude and direction from the values expected to be produced by expansion of the explosion cavity, but seem to be related to the influence of geological structures near the lakes. High-speed motion pictures indicate that the ground surface in the GZ area had risen vertically about 8 m by 1.4 sec after the explosion and had returned to within about 1 m of its original elevation by 4 sec after the explosion.