This study explores the second language (L2) acquisition of a segment that exists in learners' first language (L1) and in their L2 but that differs in its phonetic realization and allophonic patterning in the two languages. Specifically, this research tracks development in one aspect of the production of the alveolar lateral /l/ in the L2 Spanish of 85 native English speakers from various levels of study and compares L2 productions to those of native Spanish speakers as well as to learners' L1 English. Additionally, laterals produced in specific contexts are compared to examine learners' acquisition of L2 allophonic patterning, as Spanish contains a subset of the lateral allophones that exist in English. Results suggest development toward nativelike norms in the phonetic details of Spanish /l/ and in allophonic patterning. These findings have implications for existing theoretical accounts of L2 speech learning, which cannot adequately account for the learning situation examined.