<prompt> Irresistible urge to do a thing repeatedly is seen inObsessive - compulsive disorderSchizophreniaSchizoaffective disorderDepression  <response>: An obsession is defined as an idea, impulse or image which intrudes into the conscious awareness repeatedly, patient tries to resist against it but is unable to . an obsession is usually associated with compulsion and a compulsion is defined as a form of behaviour which usually follows obsessions,the behaviour is not realistic and is either irrational or excessive compulsion may diminish the anxiety associated with obsession Ref: a sho textbook of psychiatry, Niraj Ahuja, 7th edition, pg no 95 