"Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity."
The Definition has not been amended since 1948.
The correct bibliographic citation for the definition is:
Preamble to the Constitution of the World Health Organization as adopted by the International Health Conference, New York, 19-22 June, 1946; signed on 22 July 1946 by the representatives of 61 States (Official Records of the World Health Organization, no. 2, p. 100) and entered into force on 7 April 1948.See also: Wikipedia - Health (as a human condition)
Text source: http://www.who.int/about/definition/en/print.html