K. Pyragas (1992) introduced a simple and eficient control scheme, called timedelayed feedback control (TDFC), that stabilizes unstable periodic orbit (UPO) embedded in a chaotic attractor. It turned out that in the case of Pyragas' stationary feedback TDFC works only for a certain class of systems. The odd number limitation (ONL) is that any UPO with an odd number of real Floquet multipliers greater than unity (or with odd number of real-positive Floquet exponents) can never be stabilized by Pyragas' TDFC. In this paper a short survey with recent results on TDFC and ONL is presented.