Idioms play an indispensable role in communication. Knowledge of idioms is considered an indicator of proficiency. This study is aimed at investigating English as a Foreign Language (EFL) students' knowledge of frequently used idioms and the effect of learner-related factors. The participants were 218 female EFL college students at the College of Basic Education (CBE) in Kuwait. A test was designed and used as the data collection instrument to assess the students' knowledge of frequent idioms. The test scores reveal a substantially low overall knowledge in this area. The results show that Kuwaiti EFL learners have difficulty comprehending common idiomatic expressions. Additionally, the study is aimed at determining whether students' knowledge of idioms is linked to age, year of study, and/or Grade Point Average (GPA). A statistically significant difference in knowledge of frequently used idioms is evident when GPA is taken into account.