The estimated 20-year renal survival rate of immunoglobulin A (IgA) nephropathy is approx. 60%, but it is difficult to determine the 'big picture' for IgA nephropathy because a biopsy is essential for its diagnosis. Here we attempted to determine the longer and more precise renal prognosis of IgA nephropathy. We examined 310 patients with primary IgA nephropathy. Using the patients' clinical records and histological reports from our hospital and other clinics, we surveyed their renal prognoses and treatments within 1 year post-biopsy, and we sent questionnaires to the patients who had stopped visiting any hospital. We set renal death as the primary endpoint and analyzed factors related to renal death. The total patient cohort was 267: 159 males, 108 females; average age at biopsy, 37.7 years; average estimated glomerular filtration rate (eGFR), 69.7 mL/min/1.73m2; urinary protein, 1.3 g/day. The mean follow-up duration was prolonged to 13.8±8.9 years (vs. 9.2±8.5 years using only medical records). The 10- and 20-year follow-up rates were 61.7% and 27.3%. The 10-, 20-year renal survival rates were 83.6% and 72.5%. Lower eGFR, hypertension, and smoking were revealed as factors inde