Optical reach is defined as the distance optical signal can traverse before its quality degrades to a level that necessitates regeneration. It typically ranges from 500 to 2000 miles, and as a consequence, regeneration of optical signal becomes essential in order to establish a lightpath between a source-destination node pair whose distance exceeds the limit. In a translucent optical network, the optical signal is regenerated at selected nodes of the network before the signal quality degrades below the acceptable threshold. Given the optical reach of the signal, to minimize the overall network design cost, the goal of the regenerator placement problem is to find the minimum number of regenerators necessary in the network, so that every pair of nodes is able to establish a lightpath between them. In this paper, we study the regenerator placement problem and present complexity result for that.