The national shortage of available inpatient psychiatric beds has led to many emergency departments (EDs) boarding patients on involuntary psychiatric holds for hours to days. Psychiatric holds absorb ED resources, consume beds that could be used for other acute care patients, and often delay adequate psychiatric treatment. Our study sought to determine if ED psychiatric holds also contribute to increased violence in the emergency department. A secondary objective was to determine if other variables, such as weather or proximity to the first day of the month (when financial assistance funds arrive), could predict ED violence. Staff hypothesized that more assaults occur toward the end of the month as some patients desire their holds revoked around the time of monthly financial support distributions. When an assault on staff occurs an overhead code is called and logged. We reviewed 1 year of these logs and compared them to logs showing the number of psychiatric holds in the department, the maximum temperature and occurrence of rain on a given day, whether a given day was in the first or last 10 days of a month, and the total ED census of a given day. The hospital is an urban level 2 academic trauma center and regional referral center in southern California that sees 120,000 patients per year. Between May 1, 2016 and April 30, 2017, 297 assaults resulting in an overhead code call occurred in the hospital with 57 of them in the ED. 94% of the ED assaults occurred during days with 4 or more patients on a hold, compared with 6% on days with 3 or fewer holding patients (p<0.04). A logistic regression analysis that included the number of holds (4 or greater versus less than 4), the maximum daily temperature, the total ED census, whether rain occurred on a given day, and the 10-day period of the month (early versus late) showed 2 significant associations. Having more psychiatric holds (4 or more) predicted assault, even with total ED census controlled (p=0.02), and more assaults occurred in the last 10 days of the month than the first 10 (p=0.03). Weather patterns were not associated with assaults. Increased boarding of psychiatric patients in the ED is associated with increased assaultive behavior, demonstrating another adverse impact of psychiatric patient boarding. Weather failed to predict assaults but as predicted more assaults occurred toward the end of the month.