This study uses data from the American Medical Association (AMA) Physician Masterfile to describe current demographic trends among physicians specializing in adult and pediatric nephrology. The analysis shows that renal physicians are younger than the physician population as a whole. Compared with other specialty groups, renal physicians are less likely to be in patient-care activities and are more likely to be in research. In recent years, the population of renal physicians has grown at a much faster rate than the rest of the physician population. A projection analysis indicates that the adult nephrologist population will more than double in size between 1987 and 2010. Among adult nephrologists, the number of women is expected to grow much faster than the number of men. Rapid growth is expected in the older age categories, whereas the number of adult nephrologists 35 years of age and younger is expected to decrease slightly.