The U.S. clinimetric instrument, the sickness impact profile (SIP), was validated for The Netherlands. The SIP is a standardized list of 136 statements aimed at measuring changes of conduct in everyday activities due to sickness, and may be used as a measure of outcome in clinical studies. Three necessary stages of a validation study were performed: translation, assignment of weighing factors to the statements and comparison of SIP measurements in a Dutch and an U.S. open population. The findings were that a good Dutch version of the SIP is available, that there is a strong correlation between the weighing factors assigned to the statements of the Dutch and of the U.S. version, and that the SIP scores of open populations of the two countries are in agreement. The findings for the Dutch open population may be used as reference values in other studies.