Approximately 80% of prison inmates are reported to be functionally illiterate. We hypothesized that poor single word decoding (the chief feature of dyslexia) accounts for a significant percentage of that rate. We studied 253 subjects selected randomly from more than 130,000 Texas prison inmates. Among them, we conducted a cross-sectional sample survey of recently admitted Texas inmates, beginning with social and educational background and followed by an educational test battery that included measures of word attack skill and reading comprehension. Deficient performance was defined primarily as single word decoding performance that measured below the 25th percentile on the Woodcock Reading Mastery Test. We found that 47.8% of the inmates were deficient in word attack skills. Word attack skills were detected in each group defined by gender and ethnicity. Nearly two thirds of the subjects scored poorly in reading comprehension.