This study focuses on the relationship between the incidence of homicide, rage, suicide, and psychiatric hospitalization as violent behaviors with temperature, humidity, and air pressure as specific meteorological variables in the city of Mashhad, in the northeast of Iran. The data were obtained from Iran Meteorological Organization, official registry of Legal Medicine Organization and the local psychiatric hospital, March 2009 to Feb 2010 daily and were analyzed with SPSS-14 using Pearson correlation coefficient, ANOVA, and post hoc analysis tests. The rates of rage and psychiatric admission had a significant relationship with the daily mean air temperature, minimum relative humidity, maximum relative humidity, minimum daily pressure, and maximum daily air pressure (p < 0.0001). There was no significant correlation between homicide and suicide rates with any meteorological variables (p > 0.05). We concluded that, the possibility of nonfatal violence and psychiatric hospitalization would increase in hot and arid weather with low air pressure.