This longitudinal case study tracks an adult second-language (L2) learner's quality and quantity of encounters with 20 vocabulary items in an English for Academic Purposes course over 3 months. The learner completed pretest and posttest vocabulary knowledge interviews, submitted course materials and notes for analysis, and was observed during class lessons. The results show that frequency of encounters contributes more to vocabulary learning than contextual richness does. In addition, the case study data illustrate the highly incremental nature of L2 vocabulary acquisition in a naturalistic context. (Contains 15 tables and 2 notes.)