Competent allocation of recourses is a key factor for success in any development program. This Brief explores the issues related to men who have sex with men (MSM) and transgender (TG) through addressing approaches for estimating numbers of MSM and TGs in a certain region or country. It is argued that establishing a reasonably accurate estimate of the MSM and TG population within a set area is essential for planners and policymakers in designing projects. Also, the only sound way of allocating funds to a project is by first, based on evidence; determine the scale of the project in terms of target population.