We describe a sample holder assembly which can control a sample temperature in a wide range. The assembly is attached to a six-circle surface X-ray diffractometer with an ultrahigh-vacuum chamber. Samples up to 16.5 mm square can be held at constant temperatures between 50 and 1350 K with a tantalum heater on a pyrolytic boron nitride plate and a closed-cycle helium refrigerator. The accuracy of a sample temperature is <1 K in cooling. We have assessed the performance of the assembly by observing the diffraction intensities from a Si(1 1 1)-root3 x root3-Ag surface. (C) 2004 Elsevier B.V. All rights reserved.