Although Legionella is an important cause of severe pneumonia, difficulty still exists in its diagnosis. Because at least 80% of patients with legionellosis excrete the Legionella antigen in their urine, various methods have been investigated for urinary antigen detection. Specificity for these methods has been reported to be 100%, and sensitivity has been shown to vary between 70 and 100%. The advantages of these methods include ease of specimen collection, the ability to obtain large quantities of specimen for concentration, the ability to detect antigen after initiation of antibiotic therapy, and the ability to obtain results quickly. Disadvantages include the ability to only reliably detect urinary L. penumophila serogroup 1 antigen and the inability to diagnose relapse or reinfection due to persistence of antigen excretion. Of the commercially-available detection methods, the polyclonal enzyme-linked immunosorbent assay (ELISA) appears to be most efficient. Its use with routine Legionella screening procedures should be considered in target populations, with the intent of early diagnosis and antibiotic therapy streamlining.