Whether one examines the average length of hospital stay at the level of geographic areas, at the level of hospitals, or at the level of doctors, length-of-stay figures are known to vary widely. Even for hospital admissions for comparable surgical procedures among comparable groups of patients, significant length-of-stay variations have been reported. As is the case for variations in the occurrence of common surgical procedures, the overall conclusion is that large variations in duration of hospital stay associated with these common surgical procedures are the rule rather than the exception. The objective of the study is to examine whether variations in hospital medical practice, indicated by the duration of hospital stay in this study, can be reduced to differences in practice style between individual doctors within the same institutional setting or to differences in practice style between groups of doctors within the same institutional setting. The latter is assumed to be the combined effect of restrictions on the (hospital) supply side and the predilection of doctors to conform to the practice of immediate colleagues. It was found out that the variation in length of hospital stay, adjusted for patient case-mix, within hospitals is much smaller than the length-of-stay variation between different hospitals. The within hospital variation between (partnership of) doctors is in most of the cases statistically insignificant. Doctors working in more than one hospital on average choose a length of stay close to the average length of stay prevailing in the different hospitals.