This research compared 40 adults with mild developmental disabilities (DD) and 40 nondelayed adults (ND) in terms of knowledge of legal terms and court proceedings. For all of the 34 terms studied, with the exception of "police office" there were significant differences between the DD and ND groups with respect to degree of conceptual understanding of terms. Results indicate that all but 6 terms assessed (adjourn, allegation, crown attorney, defendant, prosecute, and court reporter) were well-defined by 85% or more of ND participants. In contrast, only 8 of the terms (police officer, lawyer, jail, court, lie, truth, judge, and witness) were reasonably conceptually understood by at least 75% of DD participants. Reported familiarity with terms in DD participants is not a reliable indicator of actual familiarity with terms. Results are discussed with respect to the need for education of DD individuals and legal professionals to support participation and fair treatment of DD individuals in legal situations.