BACKGROUND: The incidence of adenocarcinoma of the cervix did not decline in Western countries in the 1970s and 1980s despite the availability and use of cervical cytologic screening. The impact of improved endocervical sampling and better recognition of the cytologic precursors to adenocarcinoma during the 1990s in reducing the risk of adenocarcinoma is currently unknown. METHODS: Using records from a statewide registry, the authors compared the screening histories of 160 women with adenocarcinoma (33 microinvasive cases and 127 invasive cases) who were diagnosed between 1995 and 2001 with the screening histories of 640 control women in a matched case-control study. RESULTS: A decreased risk of invasive adenocarcinoma was associated with a recent negative Papanicolaou (Pap) smear and at least one smear with an endocervical component since 1994. An increased risk of invasive adenocarcinoma was associated with a history of previous cervical abnormalities and greater than 5 years between Pap smears. There was no significant difference between cases and controls with regard to the number of negative Pap smears. There was little apparent difference in the screening histories of patients with microinvasive tumors and the controls, with the control women appearing to have no greater relative protection than the cases. With biennial screenings, the authors estimate that a 46% reduction in the cumulative incidence of invasive adenocarcinoma could be achieved, and with annual screening, a 65% reduction could be achieved. CONCLUSIONS: The incidence of cervical adenocarcinoma should begin to decline in the current decade among screened women.