This study assessed the aetiologic and public health importance of various risk factors for cervical dysplasia. A case-control design was used in which all cases had a histologically confirmed mild, moderate or severe cervical dysplasia. Controls were sampled from the general population. A total of 257 cases and 705 controls returned a postal questionnaire about marital status, sexual behaviour and contraceptive use, smoking behaviour and dietary intake of some nutrients. An increased risk was observed for women who were smokers and women whoreported more than one sexual partner. For women who reported more than six sexual partners, the adjusted odds ratio was 11.5 (95% CI: 6.6-20.2); for women who smoked more than 20 cigarettes per day, an adjusted odds ratio of 2.5 (95% CI: 1.6-3.9) was found. Use of oral contraceptives for more than 10 years increased the risk: the adjusted odds ratio was 2.3 (95% CI: 1.2-4.5). The population attributable risk percentage (PAR%) of these three risk factors together was 72%, while number of sexual partners, number of cigarettes smoked and oral contraceptive use alone amounted to a PAR% of 57%, 29% and 8% respectively. Considering the preventive potential against the background of causality of therelationships and the social acceptability of the proposed changes, it is concluded that cervical cancer and its precursors might for the greater part be prevented by behavioural changes, such as reducing smoking and using contraceptive barrier methods.