Background: Word-finding problems commonly occur in aphasia and can significantly affect communication. Assessment of this deficit typically involves naming pictures. However, this method has been criticised as lacking ecological validity. Alternative methods include the measurement of lexical retrieval in narration or conversation, although few published studies have quantified word finding in the latter. Aims: We aimed to identify a reliable and valid assessment of lexical retrieval in conversation, and to elucidate the nature of the relationship between lexical retrieval in picture naming and in conversation. Methods and Procedures: We developed a quantitative measure of word finding in conversation in aphasia and established the reliability and stability of the method. We compared the scores of a group of people with aphasia on this measure with their scores on a picture-naming test. Outcomes and Results: We found significant relationships between picture-naming scores and a number of key variables analysed in the conversation measure. We propose that scores on picture naming relate to the ability to retrieve nouns in everyday conversation for the people with aphasia who took part in this study. Conclusions: The use of picture-naming tasks is justified, providing a valid and rich means of assessment of lexical retrieval. Further research is required to replicate these results with more people with aphasia. We offer the quantitative assessment of conversation developed here for use in research and clinical spheres.