The peculiar mesophase structure of a series of thermotropic poly(urethane-ester)s is discussed. The polymers form different nematic phases, namely a nematic mesophase with cybotactic groups and a conventional nematic mesophase. The X-ray diffraction analysis suggests that two types of structural arrangements, namely smectic C-like and conventional nematic structures, coexist inside the cybotactic nematic mesophases, to which different internal degrees of correlation correspond. The correlation length parallel to the director of the nematic mesophase ranges from 38 to 45 Angstrom. In the cybotactic groups the correlation lengths parallel and perpendicular to the director range from 260 to 560 Angstrom and 130 to 270 Angstrom, respectively.