Objectives: Idiopathic immunoglobulin A nephropathy (IgAN) is the most common and most widely studied glomerulonephritis globally. Yet the highly heterogeneous nature of this disease results in unpredictable clinical course and outcomes. In this study, we proposed to compare the outcomes of IgAN patients with or without proteinuria at the time of diagnosis. Methods: We investigated the long-term prognosis of 509 patients with biopsy-proven IgA nephropathy for a median duration of 99 (97-104) months. Of the total cohort, 243 (47.7%) patients presented without significant proteinuria at the time of biopsy (proteinuria < 0.3 g/day) and 266 (52.3%) presented with significant proteinuria. Baseline characteristics, pathologic scores using the Oxford classification and semiquantative grading and clinical outcomes after at least 5 years of follow-up were compared. Results: Among the baseline characteristics observed, there were no significant differences in parameters such as age, sex and BMI, but a higher percentage of patients with diabetes, hypertension and usage of medication such ACE inhibitors and ARBs was observed in the proteinuria group. Mean eGFR (SD) at the time of diagnosis was 89.7 (29.6) ml/min/1.73 m2 in the proteinuria group and 103.9 (23.6) ml/min/1.73 m2 in the no proteinuria group (P <0.001). Proteinuria levels were 1.12 (1.50) g/g Cr and 0.09 (0.04) g/g Cr respectively. After a follow-up period of more than 5 years, eGFR dropped in both groups, 71.4 (29.8) in the proteinuria group and 82.6 (19.9) in the no proteinuria group, but the difference in progression rate was not significant (P > 0.05). Of the patients in the proteinuria group, 5 developed dialysis-dependent ESRD and 2 patients died, while no patients in the no proteinuria group progressed to advanced CKD (eGFR below 30 ml/min/1.73 m2) or ESRD. Conclusions: The long-term outcome of IgA nephropathy patients without proteinuria on diagnosis is excellent especially compared to those with proteinuria.