This study is a mixed methods case study which examines adult second language acquisition of Spanish in the Massively Multiplayer Online Roleplaying Game (MMORPG) World of Warcraft. I follow two participants who play the game in Spanish over a period of 3-4 months, and use vocabulary- and grammar-based proficiency tests, personal interviews, and transcriptions of in-game communication to measure developments in their Spanish language proficiency. I engage with cognitive and sociocultural SLA theory to explain and evaluate their learning developments. I also evaluate the validity of applying cognitive and sociocultural SLA theory to the MMORPG-based learning context. The results indicate that language acquisition through MMORPGs is possible, and that it is dependent on certain learner- and game-specific factors. The study of these factors is an important area for future research. Finally, the study finds that the application of cognitive and sociocultural SLA theories lends itself well to the MMORPG-context.