OBJECTIVE The purposes of this study were to determine the accuracy of the immunization histories of hospitalized preschool children, assess the sociodemographic factors associated with delayed immunizations, and interview parents or guardians concerning their views on ways of improving immunization delivery. METHODS The immunization status of 215 preschool children admitted to a pediatric hospital was determined by interviewing parents or guardians regarding their children's immunization histories. The patient's immunization records were subsequently reviewed for confirmation. The admitting physician's history also was reviewed to determine whether the patient's immunization status had been noted. Finally, parents or guardians of all children studied were interviewed to assess their views on ways of improving the delivery of immunization services. RESULTS Only 44% of the 215 preschoolers evaluated were adequately immunized. Among those between 2 and 5 years of age, 52% were fully immunized. Only 17% of those who were inadequately immunized could have been completely updated if given an immunization at discharge. The admitting physician failed to document the immunization status of 22% of the patients. Thirty percent of the parents gave inaccurate information concerning the immunization status of their children. Most parents felt that the provision of transport (30%) or formal remainders (21%) would enhance immunization rates. Multiple regression analysis showed that a history of missed opportunity to immunize, male gender, lack of transportation, and lack of day care attendance were significant predictors of delayed immunization. CONCLUSIONS Resident physicians should be more stringent in documenting the immunization status of all admitted preschoolers so that those found to be delayed could be updated before discharge. A hospital policy of updating underimmunized children at discharge and reporting the immunization status of all discharged patients to their primary care provider could help improve the immunization coverage in this population. Transportation for routine health maintenance and telephone or mailed remainders might further improve the immunization status of inner-city children.