BACKGROUND: Screening by cytology is a potentially highly effective procedure for preventing carcinoma of the uterine cervix. To elucidate any weaknesses in the screening procedure in a Swedish county where screening started many years ago, the detection of invasive cervical squamous cell carcinoma was compared to the prior cytological screening. METHODS: On the basis of the complete Pathology data files, including cytology and histology, all 112 women with invasive cervical squamous carcinoma were compared to 112 matched controls from the Swedish Population Register, regarding attendance rate and results of Pap-smears prior to the date of discovery of an invasive carcinoma in the case. RESULTS: Almost as many cases as controls had a history of pap-smear testing, but the cases had significantly more prior atypias registered. Only 16% of women with cervical carcinoma and younger than 60 years were lacking Pap-smear tests prior to the carcinoma diagnosis, but 46% had former atypias registered. More than half of them presented, however, a negative Pap-smear test less than three years before the diagnosis. Among the controls, 10% were lacking prior Pap-smears and only 9% had former atypias registered. CONCLUSION: The policy for follow-up and treatment of cervical dysplasias has to be improved in order to achieve a further reduction of the incidence of invasive carcinoma.