In Illinois, school boards that initiate dismissal proceedings against a tenured teacher without a clear understanding of teacher dismissal case law risk the possibility that an underperforming teacher could be reinstated to a teaching position. The purpose of this study was to examine the history, frequency, and legal basis of tenured teacher dismissals in Illinois for the period from 1990 through 2008 in an effort to identify methods, trends and/or patterns in tenured teacher dismissal hearing officer decisions and appellate court cases. Dismissal cases generally fell into seven distinct categories: insubordination/absence, drug/alcohol misconduct, personal misconduct, sexual misconduct, physical abuse, incompetency, and lack of qualification to teach. Research found that school districts must prove that the teacher's misconduct has done damage to students or the school, and the district should, when possible, issue a warning before attempting dismissal proceedings. School districts must also strictly comply with both district and legal procedures when dismissing a tenured teacher.