In people infected with the human immunodeficiency virus (HIV) both the CD4 T-cell count and the viral load are used to monitor disease progression to acquired immunodeficiency syndrome (AIDS). CD4 counts of <500/mm(3) are associated with opportunistic infections and certain malignancies, so-called 'AIDS-defining' conditions. Highly active antiretroviral therapy, using combinations of reverse transcriptase inhibitors and/or protease inhibitors, can improve considerably the prognosis of people who are HIV-positive, but such therapy is not yet widely available in many developing countries. People with AIDS are predisposed to urinary tract infection (UTI) by uncommon bacteria and pathogens, e.g. fungi, parasites and viruses, which may affect any urogenital organ; treatment should be culture-specific and long-term, because there is a tendency to recurrence, infection with multiple organisms and resistant isolates. Voiding dysfunction in patients with AIDS is usually a result of neurological complications caused by opportunistic infections, and has a poor prognosis. Of patients with AIDS, 30-50% develop a cancer, especially Kaposi's sarcoma (KS) and non-Hodgkin's lymphoma (NHL). KS may involve any urogenital organ, but is usually part of systemic disease. Small lesions on the external genitalia can be treated with laser, cryotherapy or surgical excision, larger lesions with radiotherapy, and disseminated or visceral KS with multidrug chemotherapy. NHL may involve the kidneys, testes and retroperitoneal lymph nodes, thus obstructing the ureters, which may require ureteric stenting or percutaneous nephrostomy. NHL can be treated with radiotherapy and combination chemotherapy. Urolithiasis in patients with AIDS may be caused by indinavir, a protease inhibitor, but the more common types of stones may also occur. Fluid-electrolyte and acid-base disturbances are common in patients with advanced AIDS, secondary to vomiting, diarrhoea, malnutrition or septicaemia. HIV-associated nephropathy occurs in 10-30% of patients, and often leads to renal failure. Testicular atrophy is common, leading to infertility, erectile dysfunction (ED) and decreased libido. Treatment for ED must include counselling about strategies to reduce the transmission of HIV. The risk of HIV transmission after parenteral exposure to blood from an HIV-positive patient is relatively low (0.2-0.4%); the urologist can reduce the risk of transmission during surgery by adopting certain precautions. After occupational exposure to HIV, chemoprophylaxis with antiretroviral medication can significantly reduce the probability of HIV transmission.