This study sought to investigate the factors influencing the utilization of immunization services among children under five in Kilungu Division. The study was instigated by drop-out rates for pentavalent vaccination which had surpassed the expected level of 10% and stood at 13%. The study was cross-sectional descriptive survey that adopted cluster sampling technique. Quantitative data was collected using an interview schedule from 360 women/care takers with children under five from 30 randomly selected villages in Kilungu Division in February 2014. Data analysis was through Statistical Package for Social Scientists (SPSS). Frequency tables and charts were used in presentation of findings. C Download