Up to 31st December 1994 all cases of legally induced abortions were notified by the physician responsible for the operation to the National Board of Health and recorded in the Register of Induced Abortions. Following this data, abortion statistics will rely on data concerning induced abortions in the Danish National Patient Register, which includes information based upon the unique personal number of all patients admitted to hospitals. The completeness of the Register of Induced Abortions and the National Patient Register as to induced abortions in 1994 was assessed to evaluate the impact of the change in method of monitoring on trends in the national and regional abortion rate. The complete number of induced abortions was estimated to be the sum of the number recorded in both registers, cases recorded only in the Register of Induced Abortions, cases recorded only in the National Patient Register, and the missing number of registration of induced abortions calculated by capture-recapture methods. Of these 18,429 abortions 96.4% were registered in the National Patient Register and 93.5% in the Register of Induced Abortions. There were some regional variations. In some counties more abortions were registered in the Register of Induced Abortions and in others in the National Patient Register. Considering the change from 1995 in sources of the statistics of induced abortions, analyses of trends in the abortion rate in the early 1990s in Denmark must be evaluated with prudence.