We studied complications after hysterectomy among all women in the Danish population who had a simple hysterectomy in the period 1978-81 based on data obtained from the Danish National Hospital Registry. Among patients, with neither diagnosed cancer nor major co-surgery (n = 23,386), we identified all the complications which occurred during hospital admission from the time of surgery up to six years from that point. Within 30 days of hysterectomy 2.6% of the patients had been diagnosed in hospitals as having complications according to our definition. The corresponding figures at 90 days and two years after the operation were 3.7% and 9.4%. The most frequently observed complications were post operative wound infections and bleeding, each affecting about 2% of all operated women. Logistic regression and Cox regression were used to identify prognostic indicators of readmission with complications. The probability of readmission with complications within six years after hysterectomy was estimated at 8% among low risk patients. The most pronounced increase in risk of readmission with complication occurred among women who had been admitted to psychiatric or somatic hospitals 0-12 months before they had their uterus removed (OR in the range 1.59 to 1.83). We discuss the prevailing difficulties of comparing observational evidence from different clinical settings reported in the literature, and emphasize the importance of developing a coordinated international strategy for non-experimental assessment of medical technology.