160 Background: Cancer clinical trials (CTs) often represent the best available treatment for many patients, but little is known about the health care utilization of these patients. We examined correlates of hospitalizations and emergency department (ED) use in cancer CT patients to determine those at greatest risk for these outcomes. METHODS We prospectively collected data on patient characteristics, hospitalizations and ED use among all patients enrolled in cancer CTs at Massachusetts General Hospital in 2014. We calculated the number of hospitalizations and ED visits in the 6-month interval following patients' CT enrollment. We used linear regression with purposeful selection of covariates to identify factors associated with hospitalizations and ED use. RESULTS Of 1,218 CT patients (mean age = 58 years; 575 (47%) male), 781 (64%) were married and 851 (70%) had metastatic disease. All cancer types were represented, but hematologic cancers (21%) were most common. Within 6 months following CT enrollment, 519 (43%) and 327 (27%) had at least one hospitalization and ED visit, respectively. At any time during their cancer course, 177 (15%) received a palliative care (PC) consult. Controlling for presence of metastatic disease, PC consults correlated with both hospitalizations and ED visits. Having a hematologic cancer and being unmarried correlated with more hospitalizations and ED visits, respectively. CONCLUSIONS Hospitalizations and ED visits occur in a substantial proportion of cancer CT patients. We need to better understand reasons for these high rates of health care utilization, but the correlations with PC consults suggest that CT patients have unique supportive care needs and that PC services are being targeted to a population particularly in need. [Table: see text].