Uptake of childhood immunisation fluctuates in the UK. Convenience, access and parents' relationships with professionals influence uptake. This study explores the decision-making by parents about their children's immunisation through focus groups with analysis to identify categories of concern. Issues raised in focus groups included fear, risk, anger, worry and guilt, confusion, difficulty of decision-making and trust of professionals. The parents of completely and incompletely immunised children shared areas of concern, but there were also significant differences. There was a subset of parents of incompletely immunised children who had decided that their children would not have full immunisation, and this group had little trust in information provided by healthcare professionals. Simply providing more information is unlikely to change their decision.