Although prior research has identified negative consequences from marijuana use, some states are legalizing marijuana for medical use due to its medical utility. In 2010, the State of Arizona passed medical marijuana legislation, yet, to date, little research has been published about the specific population characteristics of medical marijuana users or their criminal activity. The purpose of this study is to present the characteristics of medical marijuana users and examine the relationship between medical marijuana use and crime, including substance use, by comparing four groups which are medical marijuana users with authorized medical marijuana ID card (authorized medical marijuana users, AuMM users), medical marijuana users without authorized medical marijuana ID card (non-authorized medical marijuana users, NonAuMM users), illegal marijuana users without authorized medical marijuana ID card (non-authorized marijuana users, NonAuM users), and non-marijuana users (Non-users). Data were collected from a sample of recently booked arrestees in Maricopa County, Arizona through the Arizona Arrestee Reporting Information Network (AARIN) project. A total of 2,656 adult arrestees participated in the study. Findings show that authorized medical marijuana users were more likely to be male, younger, and high school graduates. Medical marijuana users, on average, were likely to acquire more marijuana and spend more money on obtaining marijuana compared to non-authorized marijuana users. Whereas the authorized medical marijuana users had a higher probability for DUI and drug selling/making than non-marijuana users, non-authorized medical marijuana users had a higher probability for involvement property crime, violent crime, DUI, and drug selling/making than non-marijuana users. Authorized medical marijuana users were less likely to use meth compared to non-authorized medical marijuana users and non-authorized marijuana users. This study suggests that it is important to recognize the non-authorized medical marijuana users under medical marijuana policy as well as the DUI regulations and medical insurance.