Background/Aims: Immunoglobulin A nephropathy (IgAN) is the most common type of primary glomerulonephritis worldwide. Although several studies have identified IgAN prognostic factors in Korea, the follow-up period was insufficient to evaluate the natural history of IgAN. Methods: A total of 471 patients were diagnosed with IgAN after percutaneous renal biopsy between April 1985 and March 2003. Patients with secondary IgAN and patients with a follow-up < 10 years since their diagnosis were excluded. Thus, 184 patients were enrolled. Results: Among the 184 patients, 97 were males (52.7%) and 87 were females (47.3%). The mean age was 33.7 ± 11.5 years, and the mean follow-up period was 181.3 ± 46.3 months. During the follow up, 73 patients (36.9%) had progressed to end-stage renal disease (ESRD). The mean duration to ESRD was 98.1 ± 55.9 months. The overall renal survival rate was 60.3%, the 10-years renal survival rate was 74.3%, and the 20-years renal survival rate was 49.3%. Univariate analyses indicated that hypertension, serum creatinine > 1.3 mg/dL, estimated glomerular filtration rate < 60 mL/min/1.73 m 2 , serum albumin < 3.5 g/dL, proteinuria ≥ 1 g/day, and severe renal pathology by the Haas sub-classification were significantly associated with ESRD. When these factors were included in multivariate Cox regression analyses, only severe renal pathology by the Haas sub-classification was an independent prognostic factor for IgAN. Conclusions: Careful follow-up and treatment is recommended, particularly in patients with IgAN and severe renal pathology by the Haas sub-classification.