The purpose of this study was to examine the construct of morphological awareness and its relations to vocabulary knowledge in Adult Basic Education (ABE) students. Morphological awareness has emerged as an important predictor of children's and ABE students' reading comprehension abilities; however, there has been a dearth of research investigating the construct and potential multidimensionality of morphological awareness. First, we examined three sets of distinctions among morphological awareness measures: inflected versus derived, real words versus pseudowords, and contextual cues versus no contextual cues. A series of confirmatory factor analyses (CFAs) revealed that the construct of morphological awareness could be multidimensional, as evidenced by a breakdown of tasks including only real words versus tasks with only pseudowords. Second, we investigated whether morphological awareness and vocabulary knowledge were best represented as distinct constructs or the same underlying ability. CFAs indicated that real-word and pseudoword morphological awareness were separate factors from vocabulary knowledge. These results have important implications for morphological and vocabulary instruction in ABE programs. Moreover, the results have practical implications for researchers assessing morphological awareness because the findings indicate that different morphological awareness measures may be tapping disparate facets of the construct.