The MMR vaccine controversy centered around the 1998 publication of a fraudulent research paper in the medical journal The Lancet that lent support to the subsequently discredited theory that colitis and autism spectrum disorders could be caused by the combined measles, mumps and rubella (MMR) vaccine. The media has been heavily criticized for its naive reporting and for lending undue credibility to the architect of the fraud, Andrew Wakefield.

Investigations by Sunday Times journalist Brian Deer revealed that Wakefield had multiple undeclared conflicts of interest, had manipulated evidence, and had broken other ethical codes. The Lancet paper was partially retracted in 2004 and fully retracted in 2010, and Wakefield was found guilty by the General Medical Council of serious professional misconduct in May 2010 and was struck off the Medical Register, meaning he could no longer practice as a doctor. In 2011, Deer provided further information on Wakefield's improper research practices to the British medical journal, BMJ, which in a signed editorial described the original paper as fraudulent. The scientific consensus is that no evidence links the vaccine to the development of autism, and that the vaccine's benefits greatly outweigh its risks.

Following the initial claims in 1998, multiple large epidemiological studies were undertaken. Reviews of the evidence by the Centers for Disease Control and Prevention, the American Academy of Pediatrics, the Institute of Medicine of the US National Academy of Sciences, the UK National Health Service, and the Cochrane Library all found no link between the vaccine and autism. While the Cochrane review expressed a need for improved design and reporting of safety outcomes in MMR vaccine studies, it concluded that the evidence of the safety and effectiveness of MMR in the prevention of diseases that still carry a heavy burden of morbidity and mortality justifies its global use, and that the lack of confidence in the vaccine has damaged public health. A special court convened in the United States to review claims under the National Vaccine Injury Compensation Program rejected compensation claims from parents of autistic children.

The claims in Wakefield's 1998 The Lancet article were widely reported; vaccination rates in the UK and Ireland dropped sharply, which was followed by significantly increased incidence of measles and mumps, resulting in deaths and severe and permanent injuries. Physicians, medical journals, and editors have described Wakefield's actions as fraudulent and tied them to epidemics and deaths, and a 2011 journal article described the vaccine-autism connection as "the most damaging medical hoax of the last 100 years".