BACKGROUND: Despite the Government acting quickly to reassure parents about MMR safety following the publication of the 1998 paper by Wakefield and colleagues, MMR uptake declined. One of the reasons suggested for this decline is a loss of public trust in politicians and health professionals. The purpose of this analysis was to examine parents' views on the role the media, politicians and health professionals have played in providing credible evidence about MMR safety. METHODS: A qualitative focus group study conducted with parents living in Central Scotland. Eighteen focus groups were conducted with 72 parents (64 mothers and 8 fathers) between November 2002 and March 2003. Purposive sampling was used to ensure maximum variation among parents. RESULTS: In the period after the MMR controversy, parents found it difficult to know who to trust to offer balanced and accurate information. The general consensus was that politicians were untrustworthy in matters of health. The motives of primary health care providers were suspected by some parents, who saw them as having a range of vested interests (including financial incentives). Among the sources of evidence seen by some parents as more credible were other parents, and Andrew Wakefield who was viewed as an important whistle-blower and champion of ordinary parents. CONCLUSION: The provision of accurate information is only one aspect of helping parents make immunisation decisions. Establishing and maintaining trust in the information provided is also important. The MMR controversy may provide useful lessons for health professionals about trust and credibility that may be generalisable to future health controversies.