Thin basement membrane isease (TBMD, also known as benign familial hematuria and thin basement membrane nephropathy) is, along with IgA nephropathy, the most common cause of asymptomatic hematuria. The only abnormal finding in this disease is a thinning of the basement membrane of the glomeruli in the kidneys. Its importance lies in the fact that it has a benign prognosis, with patients maintaining a normal kidney function throughout their lives.