Tensegrity mechanisms using linear springs as tensioned elements constitute an interesting class of mechanisms. When considered as manipulators, their workspace remains however to be defined in a generic way. In this article, we introduce a workspace definition and at the same time a computation method, based on the estimation of the workspace boundaries. The method is implemented using a continuation method. As an example, the workspace assessment of a two degrees of freedom (DOF) planar tensegrity mechanism is presented.