Regulators and the scientific community are increasingly focused on patient risk from radiation exposure related to medical imaging. As a central/national database is currently lacking, emergency physicians are often reliant on patient recall of prior CT history to assess the risk/benefits of emergent imaging vs. the risk of recurrent radiation exposure. The objective of our study was to assess the proportion of patients in our population who would underestimate the prior number of CT scans that they had received previously. This was a prospective, cross-sectional study. We enrolled a convenience sample of adult, hemodynamically stable, oriented, consenting patients at an academic inner-city ED. Each patient completed a written survey providing demographic, chief complaint information, and questions regarding their imaging history. Patients’ estimates of prior CT imaging exposure were then compared with electronic records from a 6-hospital system database that includes over 80% of all ED visits within a 12-county region (2005-present). Categorical data presented as frequency of occurrence and analyzed by chi-square. Continuous data presented as means+/-SD and analyzed by t-tests. There were 298 patients enrolled; mean age 41+/-16 years, 49% female, 67% Hispanic, 35% income < $20,000, 34% < or = high school education, 14% private insurance, 43% presented for painful conditions. 39.9% (119/298) of patients underestimated their total number of prior CTs by at least one (difference = patient reported CTs - in system CTs in electronic records). The following patient characteristics were not associated with underestimation: age (p=0.08), female sex (p=0.38), less than high school education (p= 0.15), Hispanic race (p=0.47), income < $20,000/year (p=0.91). 12.4% of patients underestimated their total number of chest CTs, while 24.2% underestimated their total number of abdominal CTs. 66.1% (197/298) patients reported that they had not had any imaging outside of our hospital system. For patients with no reported outside system CTs, 35.0% (69/197) underestimated their prior CT exposure by at least one. Within the overall study group, 25.6% overestimated their total CTs by at least one. For our predominantly Hispanic, urban poor study group, emergency department patient recall for prior CT imaging history was poor. There were a significant proportion of patients who either underestimated or overestimated respectively their prior exposure.