During the past 3 decades, the combination of trimethoprim and sulfamethoxazole has occupied a central role in the treatment of various commonly encountered infections and has also been particularly useful for several specific clinical conditions. However, changing resistance patterns and the introduction of newer broad-spectrum antibiotics have led to the need to carefully redefine the appropriate use of this agent in clinical practice. While trimethoprim-sulfamethoxazole's traditional role as empirical therapy for several infections has been modified by increasing resistance, it remains a highly useful alternative to the new generation of expanded-spectrum agents if resistance patterns and other clinical variables are carefully considered. It also seems to have an increasing role as a cost-effective pathogen-directed therapy with the potential to decrease or delay development of resistance to newer antibiotics used for empirical treatment. In addition, trimethoprim-sulfamethoxazole continues to be the drug of choice for several clinical indications.