This review considers possible reasons behind parents' missed vaccination opportunities in the context of the latest immunisation coverage rates for England. Suboptimal uptake is not exclusive to measles, mumps and rubella (MMR). A substantial proportion of children also miss diphtheria, tetanus and polio vaccination. For MMR and diphtheria, tetanus and polio, uptake of primary plus booster immunisation is lower than for the primary course alone. Several reasons for suboptimal uptake are identified from the international literature. These provide insights into parental decision-making and potential barriers to immunisation that may need to be addressed in efforts to improve coverage rates.