To identify risk factors for various cervical abnormalities, 237 women with abnoromal cervical smears and 422 control women were interviewed. Cervical biopsy specimens taken from the patients with abnormal smears were reviewed according to standard criteria by one pathologist and classified as follows: 65 carcinoma in situ, 81 severe dysplasia, 44 mild dysplasia and 47 normal histology. Factors associated with risk of mild dysplasia, severe dysplasia and carcinoma in situ were similar to those previously identified for invasive carcinoma, and included age at first intercourse, multiple sexual partners and pregnancy outside marriage. Analysis to disentangle correlated factors revealed that number of sexual partners exerted effects independently of age at first intercourse, whereas the reverse was not true. This finding fails to support suggestions that adolescence is a period when the cervix is most vulnerable to the effects of sexual behaviour. Other factors relating to risk of cervical abnormalities were smoking and use of oral contraceptives. It was not possible to show that these relationships were incidental, but further investigation is required to establish whether they are causal.