Dialysis-induced hypotension, the sharp decrease in blood pressure occurring during hemodialysis, remains one of the most difficult problems associated with hemodialysis even today. However, there is yet no established theory to explain the mechanism triggering dialysis-induced hypotension. This review attempts to offer a consistent and cohesive source of information on the hemodynamics during dialysis-induced hypotension, and then analyzes etiologic factors in such hypotension reported by various investigators. Finally, three hypotheses concerning the mechanism of dialysis-induced hypotension including our own are introduced.