Millions of custodial suspects waive their rights each year without the benefit of legal counsel. The question posed to psychologists in disputed Miranda waivers is whether this waiver decision was, knowing, intelligent, and voluntary. Mental health professionals must be aware of potential barriers to Miranda comprehension to provide expert opinions regarding a defendant's competency to waive rights. The current study examined how Miranda warning reading level, length, and method of administration affects Miranda comprehension. Recently arrested detainees at Grayson County Jail were administered oral and written Miranda warnings from the Miranda Statements Scale (MSS; Rogers, 2005) to measure their comprehension of the warnings. Surprisingly low levels of Miranda comprehension were found for most warnings. For all warnings at or above 8th grade, a substantial minority (27.1% - 39.6%) of defendants exhibited failed (i.e., < 50% understanding) Miranda comprehension. Regardless of other variables, oral administrations resulted in a substantially larger number of defendants with failed Miranda comprehension. Implications for public policy and clinical practice are discussed.