In response to media scares and subsequent falls in measles, mumps and rubella (MMR) vaccine uptake, a case-control study was conducted to identify factors associated with non-uptake of the second dose of the vaccine in children resident in North Wales. Subjects were selected from parents of children scheduled for the second dose between October and December 1997. Postal questionnaires were used to compare knowledge, attitudes and practice of non-acceptors (cases) and acceptors (controls). Of non-acceptors, 92.1% (95% CI 82.2-97.5%) stated that they would allow another child to have at least one dose of MMR, and 39.2% (95% CI 25.8-53.9%) both doses of MMR vaccine. Non-acceptors were more likely to report having obtained information from newspapers/television (OR 2.04, 95% CI 1.03-4.02) or from the general practitioner (OR 2.02, 95% CI 1.07-3.86) and to report having 'a lot' or 'some' influence from newspapers/television (OR 3.52, 95% CI 1.57-7.86). The 'combination of three vaccines in one jab' was identified as a worry by 55.1% (95% CI 40.2-69.3%) of non-acceptors and 38.5% (95% CI 30.6-46.9%) of acceptors. On this evidence, catch-up campaigns would be an effective way of increasing coverage; also health professionals need tools to enable them to communicate effectively in the face of ongoing scares.