Hemodialysis patients often do not complete their full amount of time on dialysis and at times miss their hemodialysis treatments completely. However, neither the magnitude nor the potential reasons for this problem are known. The prevalence of unauthorized absences from hemodialysis sessions (no shows) and both the prevalence and reasons for early terminations from hemodialysis sessions (early sign-offs) were prospectively studied at a large hemodialysis unit in the southeastern United States. This unit provided a total of 31,212 hemodialysis sessions in a 12-month period to an average of 231 patients. There was a total of 2,108 early sign-offs (6.8 +/- 0.9%/mo) and 387 "no-shows" (1.2 +/- 0.2%/mo) during this 12-month period. The most common reasons for early sign-off were cramping (17.9%), followed by "feels bad or sick" (14.2%), personal business or errands (12.1%), lack of transportation later in the day (7.7%), and refusal to comply with the prescribed treatment time (6.4%). In sum, approximately 55% of early sign-offs were due to medically related problems, whereas most of the remainder occurred because of either personal obligations or noncompliance with the dialysis prescription. This information should be of value when designing programs intended to reduce the number of early sign-offs in hemodialysis patients.