Speaking and writing are two modalities of language production and their fundamental differences are found in the various functions they perform in communication. Some of the differences that can be found in the analyses of both modalities are related to the level of planning, lexical diversity, syntactic complexity and contextual dependance. Written language is often seen as contextually independent and allows a higher level of planning. As a result, longer and more complex utterances with higher lexical diversity are found in written language. The participants in this research were Croatian adult native speakers, mostly matched in age and educational degree. The data was collected based on two stories taken from a Multilingual Assessment Instrument for Narratives (MAIN, Gagarina i sur., 2012). The stories are controlled for cognitive and linguistic complexity and parallelism in macrostructure and microstructure. The aim of this research was to compare narrative adult discourse with regard to language modality. Differences were observed on the two measures of lexical diversity, measure of syntactic complexity, representation of content words and marking of the elements of the story. The collected data was transcribed in programme CLAN (Computerized Language Analysis) as a part of database CHILDES (Child Language Data Exchange System, MacWhinney, 2000). The statistical analysis of data was made in programme for statistic processing IBM SPSS Statistics 22. Results have shown that lexical diversity is higher in written language. However, there were no differences in terms of syntactic complexity. The representation of content words is higher in written language and there was no difference between modalities based on the story structure. The results of this research show valuable information on the differences between language modalities because this research was done in Croatian for the first time on the same participants and homogenous test materials. Furthermore, from the point of view of speech and language therapists who deal with difficulties in both modalities, it is important to know about these differences in the language of people with no difficulties in order to define their goals in evaluation and therapy of people with disabilites.