This paper critically examines the exclusive use of the relative frequency of subordinate clauses as a measure of syntactic complexity in Second Language Acquisition (SLA) L2 acquisition and as an indicator of Second Language (L2) development. Following Lambert & Kormos (2014), it is argued that it is important to also take into account: (i) different subordinate clause types, (ii) item-based frequencies, and (iii) text genre. Longitudinal written data was collected among 21 Dutch-speaking foreign language learners of Swedish. Based on these data, the study shows that the subordination ratio (a common measure for syntactic complexity) alone was found to be insufficient as an indicator of syntactic complexity and L2 development, as hardly any significant differences were observed in the subordination ratios of the learners and native speakers. The study shows that other aspects are also relevant in determining the learners’ level of syntactic complexity as well as their L2 development, such as the internal structure and context of subordinate clauses, subordinate clause types, and especially the type-token ratio of subordinators used. The results showed a significant negative correlation between the subordination ratio of texts and the type-token ratio of subordinators. The aim of the study is to acknowledge the variation in the learners’ use of subordinate clause, in addition to the general subordination ratio, in order to arrive at a more nuanced view of syntactic complexity in second language acquisition.