Since 1979, six national metrology institutes (NMI) and another laboratory have submitted 16 samples of known activity of 201Tl to the International Reference System (SIR) for activity comparison at the Bureau International des Poids et Mesures (BIPM), with comparison identifier BIPM.RI(II)-K1.Tl-201. The activities ranged from about 3.5 MBq to 207 MBq. The degrees of equivalence between each equivalent activity measured in the SIR and the key comparison reference value (KCRV) have been calculated and the results are given in the form of a matrix for six NMIs. A graphical presentation is also given. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by Section II of the Consultative Committee for Ionizing Radiation (CCRI(II)), according to the provisions of the Mutual Recognition Arrangement (MRA).