In a study on L2 proficiency in writing, conducted among 84 Dutch university students of Italian and 75 students of French, manipulation of task complexity led in the complex task to a significant decrease of errors, while at the same time a trend for a lexically more varied text was observed (Kuiken and Vedder 2005, 2007, in press). Based on this first analysis in which some global performance measures were used, a more specific analysis was carried out. In the latter analysis, which is reported in this article, accuracy was investigated in more detail according to the type of errors in the L2 texts, while lexical variation was analysed further by distinguishing frequent words from infrequent ones. Results showed that the effect of task complexity could mainly be attributed to lower ratios of lexical errors in the more complex task. With respect to the use of frequent versus infrequent words mixed results were found. On the basis of these findings a number of implications with regard to the operationalisation of task complexity and linguistic performance are discussed. (Contains 6 tables and 2 notes. Appended is: Example of a Complex Writing Task: Bed and Breakfast in Italy.)