In order to evaluate the efficacy of warfarin for the secondary prevention of cardioembolic stroke due to nonvalvular atrial fibrillation (NVAF), we retrospectively investigated the frequencies of recurrent brain embolism and hemorrhagic complications in 68 subjects (62 +/- 9 years old, 54 men and 14 women), who had experienced at least one cardioembolic stroke prior to the study period. The follow-up period was 39 +/- 27 months. Paroxysmal and persistent atrial fibrillation were seen in 37 and 31 subjects, respectively. We assigned the subjects to three subgroups according to types of the events during the follow-up; recurrence group, hemorrhage group, and non-accident group. Prothrombin time (international normalized ratio, INR) was assessed as mean value during the follow-up period. The prothrombin time at the time of recurrence and hemorrhagic complication was also taken into consideration for data analysis. Recurrent brain embolism was observed in three patients (1.4%/yr). Major bleeding occurred in 12 patients (5.5%/yr) and three of them were fatal (subarachnoid hemorrhage, brain hemorrhage, and acute subdural hematoma). The mean value of INR in the hemorrhage group (3.0) was higher than that in the recurrence group (2.2) and in the non-accident group (2.3) (p < 0.001, vs. non-accident group). The lowest mean value of INR in the hemorrhage group was 2.5. The prothrombin time in the recurrence group did not differ from that in the non-accident group. The death rate in the hemorrhage group (4/12, 33.3%) was higher than those in the recurrence group (0) and in the non-accident group (4/53, 7.5%) (p < 0.01, vs. non-accident group).(ABSTRACT TRUNCATED AT 250 WORDS)