Meitnerium was first synthesized on August 29, 1982 by a German research team led by Peter Armbruster and Gottfried Münzenberg at the Institute for Heavy Ion Research (Gesellschaft für Schwerionenforschung) in Darmstadt.
Meitnerium is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 266Mt in 1982. There are seven known isotopes, from 266Mt to 278Mt. The longest-lived of the known isotopes is 278Mt with a half-life of 8 seconds.