Granulomatous interstitial nephritis (GIN) is a rare histologic diagnosis. This series reports the presenting features, associated conditions, treatment, and outcome of patients with a diagnosis of GIN in Glasgow during a 15-yr period and compares this with the available literature. Eighteen cases were identified: Five cases were associated with sarcoidosis, two were associated with tubulointerstitial nephritis and uveitis, two were associated with medication, and nine were idiopathic. Patients presented with advanced renal failure (median estimated creatinine clearance 21 ml/min) and minimal proteinuria (urine albumin-to-creatinine ratio 9.9 mg/mmol). Sixteen patients were treated with prednisolone for a mean of 25 mo. Six patients relapsed with reduction in prednisolone dosage, and four patients required steroid-sparing agents. During the mean follow-up of 45 mo, renal function improved or stabilized in 17 patients; the rate of improvement in renal function was most marked in the first year after diagnosis with a gain in function of +1.9 ml/min per mo. The median estimated creatinine clearance at final visit was 56 ml/min. One patient required renal replacement therapy at diagnosis but recovered renal function with treatment. No patient required long-term renal replacement therapy. There was no correlation between the degree of fibrosis or inflammation on biopsy and renal outcome, and the features on biopsy did not help to determine the cause of GIN. GIN is a treatable cause of renal failure that highlights the value of renal biopsy in patients who present with renal failure even when there is minimal proteinuria. The rarity of GIN demonstrates the need for systematic data collection.