|ABSTRACT The present study focuses on the acquisition and processing of gender agreement by second language (L2) learners of Spanish, whose first language (L1; English) lacks gender. Some L2 theories argue that these learners will not be able to acquire gender, and will have to resort to different strategies to process it in their second language (Hawkins, 2009), particularly in long-distance agreement dependencies (Clahsen & Felser, 2006; Clahsen, Felser, Neubauer, & Silva, 2010). Other theories argue that it is possible for those learners to acquire gender, but they may experience difficulty accessing target gendered forms, due to the computational burden of using a second language (Haznedar & Schwartz, 1997; Prévost & White, 2000). The current study addresses these theories by investigating how native speakers and advanced L2 learners use the gender markedness information (masculine vs. feminine) conveyed by the first element in a long-distance agreement dependency in particular, to process the second agreeing element in the dependency. In addition, it is investigated whether native speakers performing a task under processing burden show similar patterns to L2 learners in their processing of gender agreement (Hopp, 2010; McDonald, 2006; López Prego & Gabriele, 2014). This latter approach attempts to test whether specific error patterns in L2 learners emerge due to processing difficulty, or to a flawed representation of the gender feature. Thus, the study contributes unique data to answer the following questions: whether advanced L2 learners can establish long-distance agreement dependencies; whether they can develop a native-like representation of the gender feature in their L2, when they lack gender in their L1; and whether they can use gender information in a native-like manner in their online processing of agreement. These questions were tested in a self-paced reading task in which a grammaticality judgment was provided after each sentence. The group of native speakers performing under processing burden was additionally asked to decide whether a string of numbers presented before each sentence was the same or different from a string presented after the grammaticality judgment was supplied. The main results of the study showed that the advanced L2 learners tested, like the native speaker control group, were sensitive to gender agreement violations in long-distance agreement dependencies. In addition, both groups revealed a significant facilitation effect from the marked (feminine) feature in their processing of long-distance agreement dependencies, crucially, in grammatical sentences. Finally, the native speakers performing under processing burden showed some weak patterns that nevertheless resembled those in the L2 learner group. Thus, the findings from the present study support theories that posit computational difficulty as the source of agreement variability in L2 learners, and run counter to theories proposing a grammatical deficit in the L2 grammar as the cause of agreement errors in learners.