The number of pregnancies terminated as induced abortions has been analysed from data recorded in the Norwegian Birth Registry and the Norwegian Abortion File at the Central Bureau of Statistics. During the time period 1 January 1979 to 31 December 1991, 871,439 pregnant women were registered. Among single women the proportion of pregnancies terminated as induced abortions varied between 40 and 75% throughout the study period. Cohabitant women chose abortion significantly more often than married women. Among married women the proportion of pregnancies interrupted varied with the woman's age and the number of children. Among women 20-34 years of age with one or no child, more than 97% of the pregnancies proceeded to term. Women undergoing abortion comprise a heterogeneous group, judged by demographic factors. Future studies must focus on social factors as well as demographic factors, in order to uncover the complexity of the reasons for choosing abortion.