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IgA nephropathy is the most common primary glomerulonephritis in adults and a common cause of end-stage renal failure. The understanding of the pathogenesis of IgA nephropathy has evolved importantly in the past few years. There has also been an improvement in the treatment of the disease. The main pathogenic characteristic of IgA nephropathy is the formation of galactose-deficient immunoglobulin A1 (IgA1), which is recognized by unique autoantibodies, resulting in the formation of pathogenic immune complexes. The complexes deposit in the glomerular mesangium and induce inflammation and renal injury. The clinical symptoms of IgA nephropathy are diverse, varying from minor urinary abnormalities to rapidly progressive glomerulonephritis. The most important prognostic factor is proteinuria. Marked proteinuria (more than 1 g per day) is predictive of poor prognosis. Another important prognostic factor is blood pressure level with the optimum level below 130/80 mmHg. Initial treatment of the disease is non-immunogenic. Angiotensin-converting enzyme inhibitors are used to reduce proteinuria and achieve better blood pressure control. In case of persistent marked proteinuria, treatment with glucocorticoids significantly improves prognosis. In case of rapidly progressive glomerulonephritis, treatment with cyclophosphamide is indicated. In this paper, we present new findings in pathogenesis and treatment of IgA nephropathy and two clinical case reports. In the first case, the patient’s abandonment of treatment resulted in rapid progression of IgA nephropathy and end-stage renal failure. In the second case, appropriate treatment resulted in improved condition and better prognosis