The ultimate strength of thin single crystals of cadmium has been measured. The crystals were initially completely free from dislocations and other imperfections, in so far as this could be established by observations with the electron microscope. They were grown from the vapor in an atmosphere of argon and had surfaces parallel to {0001} and{011¯0}planes,[2¯110]axes, and uniform rectangular cross sections. The crystals were strained in the electron microscope with a pneumatic tensile device, and the maximum elastic strain which they would sustain was determined directly from measurements of diffraction patterns. The near‐perfect crystals failed at measured elastic strains between 3.8% and 4.5% along the[2¯110]direction. The corresponding normal stress was also measured directly with the tensile device. When the elastic strain along the[2¯110]axis of tension is 4%, the resolved shear stress on the glide systems which could be activated varies betweenG/11 andG/15, whereGis the relevant shear modulus. This is within the range of estimated theoretical maximum strengths of crystals for deformation by a homogeneous shear process.