Urban, poor, preschool children are noted for having low immunization rates. To determine factors related to completion of immunization, vaccine records of 479 3-year-old children from an inner-city pediatric clinic were reviewed. Complete immunization was defined as four diphtheria-tetanus-pertussis doses, three oral polio vaccine doses, one measles-mumps-rubella dose, and one Haemophilus influenzae type b vaccine dose. Seventy percent of our patients were up-to-date by 2 years of age. The administration of all age-appropriate vaccines at a single visit for patients 15 months and older, the establishment of a continuous primary-care relationship, earlier age at first immunization, and lower birth weight were significantly associated with higher immunization levels in our study.