The closest it has ever been was 2 minutes to midnight(World War III) in 1953.
1953 The United States and the Soviet Union test thermonuclear devices within nine months of one another. (This is the clock's closest approach to midnight since its inception.)
as it stands as of Jan 14th 2007 is 5 minutes to midnight.
North Korea's test of a nuclear weapon [ 4 ] , Iran's nuclear ambitions, a renewed U.S. emphasis on the military utility of nuclear weapons, the failure to adequately secure nuclear materials, and the continued presence of some 26,000 nuclear weapons in the United States and Russia. [ 5 ] Some scientists assessing the dangers posed to civilization have added climate change to the prospect of nuclear annihilation as the greatest threats to humankind. [ 6 ]