Superconducting Tl-Ca-Ba-Cu-O (TCBCO) thin films, about 1 mu m thick, have been prepared on (100) MgO substrates using a thermal evaporation and improved two-step annealing process involving final thalliation under controlled Tl2O vapour pressure in a quartz reaction tube. The Tl2O vapour pressure was changed by adjusting the position of a Tl2O3-containing boat, thus altering the boat temperature from 740-780 degrees C when the furnace temperatures were between 830 and 850 degrees C. The superconducting properties of TCBCO films are strongly dependent on the Tl2O vapour pressure and oxygen partial pressure. Thalliated Tl2Ca1Ba2Cu2Ox and Tl2Ca2Ba2Cu3Ox films with T-co’s of up to 110 and 117 K, respectively, and J(c,77K)’s measured over large areas of up to 1 x 10(4) Acm(-2), have been obtained. A low-temperature annealing process after thalliation does not seem to offer significant advantages for these films, which is thought to be due to the loss of thallium. It is also found that measuring J(c) values on narrow microbridge structures can give a false impression of the overall quality of polycrystalline thin-film samples.