Complicated urinary tract infection occurs in the setting of a functionally or structurally abnormal genitourinary tract. Many different abnormalities may lead to a designation of complicated urinary tract infection, and these abnormalities will have different influences on the frequency of infection and likelihood of relapse or reinfection. The microbiology of complicated urinary tract infection is characterised by a greater variety of organisms and increased likelihood of antimicrobial resistance compared with acute uncomplicated urinary tract infection. Appropriate management requires a urine specimen for culture prior to institution of antimicrobial therapy, and ensuring that the underlying abnormality is fully characterised to determine whether it can be corrected. A wide variety of antimicrobial agents are effective for treatment, and are usually given for 7 to 14 days. If the underlying abnormality can be corrected, subsequent infections may be prevented. However, if the underlying abnormality cannot be corrected a high recurrence rate of infection, approaching 50% by 4 to 6 weeks, is expected. Further study of complicated urinary tract infection is necessary, including determination of when asymptomatic bacteriuria warrants treatment, and exploration of nonantimicrobial approaches to management.