Media reports in 1998 of a possible link between the combined measles, mumps, and rubella vaccine (MMR) and autism or bowel disease have made many parents question the vaccination. Understanding their concerns and being familiar with the current scientific evidence about the safety of MMR are important if physicians are to allay doubts about the vaccine. Many parents worry that MMR may cause autism or bowel disease. But the UK Department of Health, the World Health Organization, and UK medical establishments—such as the British Medical Association and the medical royal colleges—do not believe that MMR is linked to these conditions. They give several reasons.