Background: Immunization against childhood disease is one of the most cost effective public health interventions available and has saved the lives of millions of children in the past three decades. Immunization also prevents many more millions from suffering debilitating illness and lifelong disability. Achieving and maintaining high level of immunization among children is necessary for the control and elimination of the major preventable diseases of childhood. Objectives: A present study was conducted to assess the immunization coverage and the impact of socio-demographic profi le on that in an urban slum area in Mumbai city. Material and Methods: A cross-sectional study was carried out in the fi eld practice area (cheetah camp urban health centre) of the T. N. Medical College, Mumbai during the period of January 2007 to October 2008. A total of 352 children from cheetah camp area in the age group of 12–23 months during the study period were selected by using lot quality technique. Results were analyzed using Statistical Package of Social Sciences (SPSS) version 13.0. Results: In the present study, out of the 352 children taken in to consideration, 55.40% were males and 44.60% were females. The overall coverage of immunization in the urban slum area was 88.07%. The most common reasons for not immunizing the child were: due to the visit to native place/village (14.00%), child was ill, hence not brought (8.20%), unaware of need to return for second and third dose (5.70%), and mother too busy (5.00%). Conclusion: In this study, as the overall coverage of immunization among the urban slum area is good but still it has pockets of non-immunization. Hence, more vigilant surveys should be conducted so that these pockets are identifi ed properly and proper actions can be taken.