Syntactic complexity, broadly defined as the range and sophistication of grammatical structures (Ortega, 2015), is a frequent focus of analyses on second language (L2) writing. This characteristic is subject to variation depending on a number of factors such as task (Ortega, 2000), instructed development (Mazgutoma & Kormos, 2015), and first language (L1) influences (Lu & Ai, 2015; Neff, Dafouz, Díez, Prieto, & Chaudron, 2004). However, with regard to this last factor, insufficient research attention has been lent to same-writer bilingual analyses, which are needed to account for individual cross-rhetorical transfer. This has limited the findings of previous studies and may obscure the true sources of maturational attainment and constraints in L2 writing, the characteristics of which may be influenced in important ways by L1 writing that at the university level is still in a state of change and development (Staples, Egbert, Biber, & Gray, 2016). The present study performs a same-writer bilingual analysis of L1 English-L2 Spanish students (N = 11) enrolled in university Spanish coursework. Results for two measures of syntactic complexity (clauses per T-unit; relative clause type distributions) suggest that certain L2 writing characteristics may be largely derived from L1 writing.