This article presents studies on the long term pumping behavior of a cryopump. It is shown that the pumping speed does not deteriorate on a time scale of 4200 s for a gas load of 2.4 x 10(5) torr 1, corresponding to similar to 10(6) ML of hydrogen. It has also been observed that the need for regeneration of the pump is dictated by the safety limits of operation rather than its pumping capability., No sudden boil off of the cryogen takes place during the regeneration phase. (c) 2007 American. Vacuum Society.