By using adaptive optics to correct the wave-front distortion of a 21-fs, 0.7-mJ, 1-kHz laser, we are able to focus the pulses to a 1-mu m spot with an f/1 off-axis parabolic mirror. The peak intensity at the focal position is 1.5 x 10(18) W/cm(2), which is to the authors' knowledge the first demonstration of generating relativistic intensity at a kilohertz repetition rate. (C) 2000 Optical Society of America OCIS codes: 140.7090, 320.7160.