Familiarity with renal issues that can challenge the care of patients with human immunodeficiency virus (HIV) should expedite diagnosis and therapeutic interventions. Among the most common problems are electrolyte and acid-base imbalances from many opportunistic infections or their treatments, including hyponatremia, hyperkalemia, hypokalemia, and hypo- and hypercalcemia. Acid-base disturbances, simple or mixed, can be due to underlying sepsis, opportunistic infections, or the therapy thereof. A recent report of seven patients with HIV with type B lactic acidosis failed to identify a satisfactory etiology. Elevations in creatinine or diminishing urine output should alert the physician to the possibilities of prerenal azotemia or acute tubular necrosis, which can result from progression of prerenal azotemia or can occur secondary to administered nephrotoxins, such as certain antibiotics and radiocontrast agents. Agents associated with nephrotoxicity include aminoglycosides, antifungal, antiviral, and radiocontrast agents, and nonsteroidal anti-inflammatory pain medications. Although prerenal azotemia and acute tubular necrosis are the most frequent causes of acute renal failure, the differential diagnosis should include acute interstitial nephritis, obstructive nephropathy, and glomerulopathies such as hemolytic uremic syndrome, thrombotic thrombocytopenia purpura, the newly described IgA nephropathy, and, in certain populations, HIV nephropathy.