Idioms such as break a leg and piece of cake make up a significant portion of spoken and written discourse. Like other linguistic expressions stemming from conceptual metaphor (e.g., metaphors, similes), idioms serve to provide understanding of one concept in relation to a different concept (e.g., love is a journey). The ability to comprehend figurative expressions has an extended developmental period that begins as young as 5 years and continues into adulthood. The Language Experience Hypothesis attributes figurative language competence to meaningful exposure to figurative expressions. The Global Elaboration Hypothesis, however, proposes that figurative language comprehension depends upon skills needed for general text comprehension (e.g., ability to make inferences, semantic knowledge). Studies with children and adolescents have shown that reading comprehension relates to both idiom familiarity and comprehension. Similar studies have not been conducted with adult struggling readers. This study examined idiom familiarity and comprehension of adult struggling readers (N = 60; M age = 41 years) in relation to their reading skills. The Idiom Familiarity and Idiom Comprehension tasks developed by Nippold and colleagues (1993, 2001) were used, which allowed for comparisons between the performance of adult struggling readers in this study and past research. Participants’ idiom comprehension scores were lower than those of adults studied in previous research, and comparable to those of children reading at similar levels. Their familiarity rankings of individual idioms aligned with the levels established by Nippold and Rudzinski (1993); however, they were less familiar with idioms than the twelfth grade group. Results from a familiarity (high, moderate, low) x context (isolation, story) ANOVA showed story context helped adult struggling readers comprehend more high-familiarity idioms, but hindered comprehension of low-familiarity idioms. Hierarchical regressions revealed that reading comprehension accounted for unique variance over and beyond idiom familiarity and word reading skills for idioms presented in both isolation and story contexts. Findings from this study contribute to the study of figurative language comprehension by examining adults with limited literacy skills. Similarly, these findings contribute to the field of adult literacy by providing initial evidence of adult struggling readers’ familiarity and comprehension of idioms.