Cervical neoplasia in pap smears: risk of cervical intra-epithelial neoplasia (CIN) after negative or no prior smears in a population without a mass screening programme. 
The aim of this study was to examine, in a population not submitted to mass screening, the risk of cancer and cervical intra-epithelial neoplasia (CIN) in Pap smears from women without previously reported positive smears.  In a logistic regression model consisting of 58,271 smears from 40,536 Norwegian women the risk of cytologically indicated CIN was studied according to age and time elapsed since last smear.  The risk of CIN was highest in smears from women with no previously registered smears and in smears taken after an interval of > or = 5 years.  Odds ratio for CIN I-II adjusted for age was highest in first time smears and in smears taken after an interval of 5 years.  Odds ratio for CIN III was highest in first registered smears.  No difference in risk of CIN III was found in smears taken within one year or 2-3 years after the last smear.  The increased risk of CIN III in first smears was most pronounced in postmenopausal women ( > 50 years).  Nine of 16 cases with cytological indication of cancer were found in women having a smear taken for the first time.  All cases with malignancy in smears were > 50 years.  The risk of cytologically diagnosed premalignant cervical conditions increases with time since the previous smear, but more than 5 years have to elapse before the risk is comparable with that in first smears taken.  Postmenopausal women without previous smears run the highest risk of serious cervical premalignancies and cancer.