CroatiaSelf-assessment ratings across single or multiple linguistic domains represent one of the methods for assessing bilingual language knowledge (Treffers-Daller, 2015). However, selfassessment scores alone might not be the most appropriate assessment tool (Zell & Krizan, 2014, Treffers-Daller 2015, thus more comprehensive indices are needed, combining subjective and objective measures (TreffersDaller and Korybski, 2015). This approach is being developed in the present study, combining self-assessment data and language sample analysis, aiming at providing an insight into the multilingual Istrian reality.Measures of lexical diversity and syntactic complexity have been used to determine whether they reflect self-assessment of language proficiency of 30 functional multilingual speakers of Croatian, Chakavian, Italian and Istrovenetian across four language skills. Participants' data was extracted from the Istrian spoken multilingual corpus (Hržica, Poropat Jeletić, Moscarda Mirković, in preparation), created using the conversational sampling method. Measures of lexical diversity (moving-average type-token ratio -MATTR; Covington & McFall, 2010) and syntactic complexity (mean length of communication unit -MLCU) were calculated using the Computerized Language Analysis (CLAN -MacWhinney 2000).The average self-assessment score positively and moderately correlated with MLCU (r(30)=.513, p<.005). MATTR did not correlate with the average self-assessment score, but the results did point to a trend (r(30)=.351, p=0.57). The Spearman rank correlation was calculated for individual domains of self-assessment. MATTR showed weak positive correlations with self-assessment of comprehension (rs(30)=.364, p<.05) and speaking (rs(30)=.388, p<.05), but not with self-assessment of reading and writing. MLCU showed moderate positive correlations with self-assessment of reading (rs(30)=.484, p<.05), writing (rs(30)=.563, p<.005) and weak positive correlations with speaking (rs(30)=.373, p<.05) and understanding (rs(30)=.364, p<.05).The correlation of language measures with self-assessment reveals that these measures are connected, showing that speakers, in this case multilingual speakers of different educational status and employment, might be able to make objective assessments of their language knowledge.