To determine the immunisation status of hospitalised infants and to examine the potential risk factors associated with incomplete immunisation. Prospective study of infants admitted to a paediatric hospital in Kuala Lumpur, conducted by interviewing carers. Twenty-two percent of infants had incomplete immunisation. The most significant factor that was associated with incomplete immunisation was the carer's lack of knowledge on the timing of the next immunisation (p = 0.005). Other factors that had significant association were the presence of a previous admission to hospital (p = 0.03) and the infant's age of more than 6 months (p = 0.025). The rate of incomplete immunisation in the study population was 22%. An admission to hospital of an infant should be taken as an opportunity to update their immunisation in order to improve the rate of uptake.