We performed transmission X-ray diffraction (TXD) experiments with a Si(1 1 1) sample and an image plate in air. A large number of crystal truncation rod (CTR) scatterings can be collected all at once in transmission geometry by suppressing thermal diffuse scattering from a bulk. This benefit makes us free from time-consuming measurements in surface X-ray diffraction. In addition, intensities along CTRs were obtained correctly. Further progress in TXD under an ultra-high vacuum condition is also discussed with the results obtained from a Si(1 1 1)-7 x 7 surface. (C) 2004 Elsevier B.V. All rights reserved.