This research investigates US Food and Drug Administration review intervals in the United States from 1997 through 2002 for three main categories new drugs applications: new drug application (NDA), the supplemental new drug application (SNDA), and the abbreviated new drug application (ANDA). Review interval for each application was the basis for evaluation and was calculated based on the difference between approval date and the application date. The median review time for all applications was 13.5 months (1.1 years). The median review intervals for ANDAs, NDAs, and SNDAs were 19.1, 12.0, and 10.0 months (1.6, 1.0, and 0.8 years), respectively, during the period. It was found that the median review period for an ANDA was significantly longer than that for an NDA and SNDA. Comparison of application class medians revealed significant differences for all 3 pairwise comparisons (all P < 0.001, Tukey HSD). Within each application category, we compared differences between years. The year effect was not statistically significant for ANDAs or NDAs. NDA median review times were 13.7, 12.0, 12.0, 10.8, 12.5, and 11.7 months (1.14, 1.00, 1.00, 0.90, 1.04, and 0.98 years), while ANDA median review times were 20.4, 19.1, 19.9, 18.6, 18.4, and 21.5 months (1.70, 1.59, 1.66, 1.55, 1.53, and 1.79 years) for 1997, 1998, 1999, 2000, 2001, and 2002, respectively. Year differences were significant for SNDAs (P < 0.001). The primary source of this difference was a lower median review time during 1997, but there was little difference in median review times for the remaining years.