This study estimates the patent life of new molecular entities (NMEs) approved by the U.S. Food & Drug Administration (FDA) in the period 1980-1999 and analyzes the relationship between generic competition and patents listed in the FDA's Orange Book. A model was developed to describe and analyze the NME's patent life. A total of 340 NMEs were included in the analysis. The results of the study demonstrate an increase in post-new drug application patent time in the 1990s. Several factors explain this increase including reduction of the new drug application review time, pharmaceutical patent extensions, pediatric exclusivity, and changes in patent statutory term.