During a mass immunisation campaign following an outbreak of measles in a Roma community settled in the town of Pulawy, Poland, we performed an estimation of the size of this Roma population and an assessment of its vaccination uptake. We obtained a list of Roma residing in Pulawy from the local municipality and estimated using a simple capture-recapture formula that Pulawy had 377 Roma residents (43% under 20 years old), which was 27% more than the 295 registered at the municipality. During the vaccination campaign, demographic information was recorded that could be linked to information from the municipality list as well as to prior immunisation status. Among the people whose data were recorded during the vaccination campaign, 14% were not registered at the primary healthcare centres, and were therefore deprived of access to healthcare. Among 102 screened subjects under the age of 20 years, 51% were vaccinated according to schedule. Vaccine uptake for the first dose of measles-containing vaccine was 56% (54/96) and for the second dose 37% (18/49). The present study indicates the need to get a better demographic overview of Roma communities living in Poland and to understand the barriers limiting their access to healthcare and social services. Organisation of catch-up immunisations of this vulnerable population is necessary.