Metronidazole is a bactericidal antibiotic with strong activity against most anaerobes and certain parasites. The drug has excellent bioavailability and good penetration in most tissues, including the cerebrospinal fluid and brain abscess contents. It is usually well tolerated with few side effects. With a few exceptions, the percentage of anaerobes, including B. fragilis group, that are resistant to metronidazole remains low. Metronidazole has been used extensively in clinical practice for years, and its uses have expanded. Its exact role in the management of Crohn's disease and entities related to H. pylori is evolving.