Aim: To describe the effect of introducing the CISOE-A framework for reporting cervical cytology results, including changes in repeat and referral advice in the Netherlands, on the efficacy of the screening programme. Changes in the distribution of cytological results, the detection rate of cervical intraepithelial neoplasia (CIN) lesions, and the detection rate of squamous cervical carcinoma are reported. Methods: The results of all gynaecology cytological and histological examinations, as registered in the nationwide database for histopathology and cytopathology (PALGA) from 1990 to 2000, were retrieved from seven laboratories in the greater Amsterdam area. Results: After the introduction of the CISOE-A classification, cytological results with equivocal diagnoses decreased significantly from 11.3% to 2.6%, without an increase in the percentages of moderate dyskaryosis or worse. During the study period, the detection rate of histologically diagnosed high grade CIN lesions increased significantly from 4.1 to 6.4/1000 smears, whereas there was no change in the detection rates of low grade lesions or invasive cervical cancer. Conclusions: The introduction of the new CISOE-A classification system resulted in a substantial decrease of equivocal results and repeat recommendations, without a decrease in the detection rate of high grade lesions, making the screening programme more efficacious.