Acute urinary tract obstruction can cause acute kidney damage and urinary tract infections, which can lead to potentially fatal complications. Although rare, acute urinary tract obstruction can be caused by compression of the gastrointestinal (GI) tract. Some cases of acute urinary tract obstruction by giant fecalomas caused by chronic constipation have been reported in patients with immobility and dehydration. 1) In addition, constipation and fecal impaction are common clinical problems in older adults. 2) Even with its clinical relevance, chronic constipation is rarely suspected as a predisposing cause of urinary tract obstruction. To date, there have been no reports of fecaloma-related acute hydronephrosis owing to chronic constipation in Korea. Here, we report a case of acute hydronephrosis owing to a giant fecaloma in an older patient. CASE REPORT An 83-year-old woman with a fever presented to the emergency room. She had a 10-year history of chronic constipation and was in a Hydroureteronephrosis with acute urinary tract obstruction can lead to serious complications such as obstructive nephropathy or pyelonephritis. We report the first case of hydroureteronephrosis caused by a giant fecaloma in an 83-year-old woman accompanied with chronic constipation in Korea. The patient with a fever presented to the emergency room and was diagnosed with right hydronephrosis. Computed tomography revealed a markedly dilated rectum with a giant fecaloma compressing the right vesicoureteric junction. Hydroureteronephrosis was resolved through manual disimpaction of the fecaloma and simultaneous lavage with rectal tubes, which improved the acute pyelonephritis and renal function. Chronic constipation can lead to giant fecaloma threatening urinary tract patency, especially in older patients with immobility or dehydration. Therefore, clinicians should consider this condition as a rare but possible cause of hydronephrosis in older patients with chronic constipation.