This article evaluates the translocation of the explosive hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) in hybrid poplar trees (Populus deltoides × nigra, DN34) grown in hydroponic solutions. Mass balances with [U‐¹⁴C]RDX were used to assess RDX translocation. Up to 60% of the RDX uptaken by the tree accumulated in leaf tissues. Analysis of plant extracts by high‐performance liquid chromatography equipped with radiochemical detection indicated that RDX was not significantly transformed during exposure periods of up to 7 d. The bioaccumulation of RDX may be an important concern for phytoremediation efforts.