In the ongoing 10th revision of the International Classification of Diseases, the WHO's rules for registering causes of death are revised. Previous studies have shown that deficiencies in the WHO's rules and basic concepts for registering causes of death impair the quality of cause-of-death statistics. The purpose of the present paper is to elucidate some of these shortcomings and to make suggestions for improvement. Also, the purpose of the WHO's definition of 'the underlying cause of death' is discussed, and a modification suggested. Suggestions are also made for new definitions of the four basic WHO concepts, 'causes of death', 'the underlying cause of death', 'direct cause' and 'contributory conditions'. At the end an account is given of the proposals made within the WHO for changes in the rules for registering causes of death.