Syntactic complexity (i.e. the grammatical sophistication exhibited in language production) has been found to be positively correlated with formality. In viewing formality as a cline rather than as a dichotomy, the present study revisits previous claims about (in)formality in learner writing in relation to syntactic complexity. The use of commonly utilized measures of syntactic complexity is explored in learner writing and across four registers from the British National Corpus (academic prose, popular science, news and fiction). The results show that while the learners generally exhibited appropriate register awareness, there were some differences noted between their writing and that of the published writers, in particular with regard to the measure of complex nominals. A detailed analysis of this measure in the academic register showed that the learners make less frequent use of adjectival and prepositional modifiers than the expert writers. Our results thus confirm previous claims about the importance of phrase-level complexity measures as a predictor of formality. It would seem that learners would benefit from some targeted instruction of such structures for increased register awareness.