A cross-sectional study was conducted in a rural area of Anand District, Gujarat to measure the efficiency of immunization sessions and to identify the reasons for missing a vaccine in a session. Caregivers of infants aged less than one year and in need of any vaccine as per routine immunization schedule were interviewed by a house-to-house survey after immunization session was completed. Efficiency of immunization session was 66.7%. Reasons for 'missed' vaccination were prior reminder not given (32.9%, P<0.01); mother's forgetfulness (26.6%); unavailability of vaccine (15%). Higher birth order (OR=2.86; 3.16-2.56), mother's current residence at father's home (OR=3.17; 3.53-2.81) were associated with 'missed' vaccination. There are barriers in health care system such as lack of prior reminder and unavailability of vaccines which should be assessed and eliminated.