This prospective study reports the immunization status of uninsured or Medicaid-funded, high-risk urban preschool-aged children hospitalized at the District of Columbia General Hospital in Washington, DC, and the reasons for delays as identified by their parents or guardians. There were 602 consecutive admissions of preschool-aged children over a 29-month period. One hundred seventy-five questionnaires were adequately completed for analysis. Thirty-four percent of parents cited problems that have social implications as the main reasons for their children's lack of immunizations. It is important to note that missed opportunities by health-care providers also contributed to the immunization delay in this patient population. Based on these results, it is important that each patient encounter be used to ensure parent education so that each child is appropriately immunized.