The nation-wide register of hospital discharges in Norway includes ICD-9 and national procedure codes. Hospitals were asked to check five surgical procedures listed in the register against the primary data sources. 649 discharges were controlled. The response rate was 68%. The results indicate that the quality of the data in the register varies for the different procedures. For procedures with high volume (resection of rectum), the error in the register is 3%. This is the same as reported from other Nordic countries. The proportion of errors in the register was high in hospitals with only one registered procedure code. The quality of data can to some extent be checked on the basis of DRG coding (DRG group 468/477). Quality control of register data is required when the number in DRG 468/477 is high in the nation-wide register or when the number of specific procedures in hospitals is low.