Mixed-symmetry assignments are made to the 1.570 (11+), 1.573 (23+) and 1.659 (31+) MeV levels in 200Hg. The characteristics of the 23+ level are shared with nearby 2+ levels at 1.254 and 1.593 MeV. An interacting boson approximation (IBA-2) analysis examines the sensitivity of the mixed-symmetry states to the xi i parameters of the Majorana term and finds that both the magnitude and sign of the delta (E2/M1) mixing ratio of 2+-21+ transitions are well reproduced at the values of the xi i parameters used to obtain a level energy fit. The IBA-2 calculations also give a satisfactory fit to the energy levels and in general provide X(E0/E2) values close to the experimental data. These calculations agree with the known oblate deformation of the ground state which is found to be predicted by Kumar's (1984) dynamic deformation model. Experimental data from n, gamma gamma ( theta ) experiments together with internal conversion coefficient (ICC) results allow 1+ levels to be unambiguously established at 1.570, 1.631, 1.718, 2.061, 2.370, 2.640 and 2.979 MeV. The measurements also provide precise delta values of many transitions while event-by-event coincidence information permits the decay scheme to be developed with previous unlocated transitions now firmly assigned.