The study used fifth-grade-level performance on the Test of Adult Basic Education (TABE) as its standard for functional literacy. Such fifth-grade literacy is considered sufficient to enable a prisoner to write a letter to a judge in which the facts of his/her case are stated. The TABE test is used to assess all Michigan prisoners' academic levels at intake, and the test is repeated 1 year later to determine further programming needs. This study presents TABE data on the reading levels of Michigan prisoners both at intake and during the course of their incarceration. These data were compared with previous claims on prisoner literacy in the relevant literature and in the testimony of Dr. Terry Kupers. In his testimony in the court case of Cain v. Michigan Department of Corrections (April 1997), Kupers stated that "40 to 80 percent of prisoners are functionally illiterate, unable to write a letter." He later (1999) amended this statement as follows: "A large number of prisoners are functionally illiterate (meaning, for instance, they would be unable to write a letter explaining a billing error)." The current study found that only 10-11 percent of Michigan prisoners given TABE tests in each year from 1997 through 2001 had literacy scores below the fifth grade; and 60 percent of prisoners under age 60 at intake had at least some high-school instruction. Comparisons with similar national data and data from other States and countries show similar results. Published claims on prisoner illiteracy that show it to be significantly more prevalent are found to have such serious methodological flaws as to be invalid. Thus, the persistent belief in the prevalence of illiteracy among prisoners is a myth. 1 table, 2 figures, and 12 references