This study reports on an investigation of reliability, different aspects of validity, and discrimination power of the C-Test as a measure of overall language ability. A C-Test developed by the researcher and a Michigan Test of English Language Proficiency (MTELP) were administered concurrently to 144 university students. The reliability coefficients found for the C-Test were high. The C-Test also proved to have acceptable content relevance and fairly high criterion-related validity. Results of two factor analyses confirmed that the C-Test texts measure, to a large extent, the same underlying trait as the MTELP –significant evidence of construct validity for the C-Test. However, the C Test texts did not prove to behave consistently with examinees of different proficiency levels. Also, it came out that the C-Test could not consistently classify the subjects in their appropriate proficiency levels. This finding was further affirmed by an ANOVA whose results demonstrated that the C-Test had difficulty discriminating between participants of lower and upper intermediate levels.