The relationship between sentence comprehension and grammaticality judgment was examined for both neurologically intact and agrammatic aphasic subjects. Aphasic subjects were able to make grammaticality judgments and comprehension judgments, but were less accurate than healthy control subjects. However, the tasks appeared dissociated for the aphasic subjects: Both the effects of semantic cues and the hierarchy of difficulty of sentence types differed across the two tasks. Further, the findings suggest that not all aspects of morpho-syntactic processing may be equally disrupted in aphasia. The results argue against both a central deficit view of agrammatic aphasia, and a view suggesting that syntactic processing is intact whereas semantic or thematic mapping is not. Instead, the results indicate that the respective performance domains of comprehension and grammaticality judgment may draw on different processes and/or operate on different aspects of the language input.