The original research by the Teotihuacan Mapping Project (TMP) identified a large number of obsidian workshops within Teotihuacan based on surface concentrations of production debris. Clark (1986b) questioned the validity of these identifications and called for subsurface excavation to confirm the presence of in situ workshop locales. This article summarizes the results from the excavation of one of the obsidian workshops identified in the Tlajinga district of Teotihuacan at Compound 17:S3E1 (Compound 17). We describe the excavations, discuss the lithic technology, and examine the subsurface contexts in terms of what they tell us about in situ obsidian craft activity. Excavations confirm that Compound 17 was a locus of large-scale obsidian craft production during the Classic period. While only a single test case, these results suggest that surface remains at Teotihuacan can be a useful guide in identifying craft production areas when they are confirmed through subsurface testing.