Modern views of the pathogenesis and natural history of nephrotic syndrome have changed substantially since the early studies by Cotugno and Bright. Contrary to beliefs held 20 years ago, we do not possess a unique satisfying explanation for the induction, maintenance, and resolution of nephrotic edema, and many concepts firmly established as "classic" are now being revised or reconsidered. These include the relationship between urinary protein losses and hypoalbuminemia, which is complicated by several factors such as daily protein intake, albumin catabolism, and the possible role of albumin loss at extrarenal sites. The influence of lowered plasma albumin on the decrease in plasma volume is also quite complex, due to technical difficulties in measuring plasma volume and turnover of radio-labeled albumin. The most contentious areas are how sodium and water retention are initiated and maintained and the relationship between hypoalbuminemia, plasma oncotic pressure, and edema. While aldosterone excretion and plasma concentrations are elevated in nephrotic patients, data on the renin-angiotensin system are controversial and the renal handling of sodium is related to a host of factors including glomerular filtration rate, altered proximal tubular reabsorption, and the role of vasodilators or vasoconstrictors. The complications of nephrotic syndrome are protean and relatively common. Among those are acute renal failure, thrombosis, infections, and hyperlipidemia. Since the introduction of percutaneous biopsy, the spectrum of lesions underlying nephrotic syndrome has widened considerably, the most common being minimal change, especially in children. There are very few prognostic indicators by which response to treatment may be predicted and these include persistent microscopic hematuria.