This paper aims to present the findings of clinical linguistic analysis on narrative speech in aphasia. Aphasia is an acquired language disorder caused by brain lesions and it can be distinguished into non-fluent and fluent aphasia. Both categories show linguistic deficits affecting language production and/or comprehension. Aphasic narrative speech is considered particularly impaired in aphasia in respect of morphosyntax and semantics (Goodglass, Kaplan, Barresi 2001). Thus, in this study, the semantic abilities of four aphasic Greek speakers, two with non-fluent and two with fluent aphasia, were examined during storytelling. The samples were analyzed semantically with the use of PRISM (Crystal 1992). The results showed the semantic abilities of the participants both at a lexical level and at thematic structure level.