Purpose of the Study: Use archived public data from Arizona to explore relationships among selected institutional and resident risk and situation-specific factors and complaints and substantiated allegations of various types of mistreatment in assisted living facilities (ALFs). Design and Methods: An exploratory/descriptive 2-group design was used. Facilities in the complaint group were identified from narrative data that appeared suspicious for mistreatment based on definitions for physical, verbal, psychological, medication, sexual abuse, neglect, financial exploitation, and physical restraint. Facilities in the comparison group were those that had no citations or complaints in 2007-2008. Narrative data were content analyzed, and chi-square analysis was used to answer 3 research questions. Results: The complaint group was comprised of significantly more assisted living centers, large facilities (51-101+), facilities licensed to provide personal care services, and facilities owned by national corporations. Substantiated allegations were significantly more frequent in assisted living centers, facilities with more than 51 beds, and those owned by national corporations. Facility risk factors were related to some types of substantiated mistreatment and not others. Implications: Findings suggest the need to evaluate use of only unlicensed assistive personnel in facilities, increase oversight of care by professional nurses, rethink the practice of not licensing small facilities, and monitor more closely practices and procedures in facilities operated by national corporations.