Production defects and external perturbations cause standard telecommunication fibers to be randomly birefringent. Fiber birefringence is the origin of the well-known polarization mode dispersion (PMD), which degrades system performances. The knowledge of birefringence properties may be crucial, especially when problems like development of low-PMD fibers or PMD interaction with optical nonlinearities in very high-capacity systems are faced. Some techniques are known to measure birefringence, and useful results have been obtained for both installed and wound-on-drum fibers. However, measurement of the circular component of birefringence still presents difficulties. In this paper, a new method for circular birefringence measurement is proposed that applies to long single-mode twisted fibers. The technique is based on polarization-sensitive optical time-domain reflectometry. Experimental results are in good agreement with the theoretical analysis.