Age determinations utilizing the U/Pb method have been carried out on radioactive minerals in the Precambrian bedrock of Sweden. As a result, minerals from northern Sweden have been found to have an age of 1775–1845 m.y. but a more precise result could not be obtained. The pegmatites in the Östersund—Sundsvall area and the pegmatites and aplites in southeastern Sweden are 1380 and 1745 m.y. old respectively. A pegmatite associated with the Karlshamn granite and a granite on Romeleåsen each have ages of 1455 m.y. Some previously determined K/Ar ages are discussed and it is concluded that the uplift of the gneiss block in southwestern Sweden occurred during or after a period of igneous activity in western Sweden 935–1000 m.y. ago. The age data also indicate a contemporaneity between the deposition of the Dal formation in western Sweden and the Jotnian sandstones, the former being of marine lithology, the latter representing a terrestrial facies.