In many developed countries, the incidence of cervical cancer has decreased. These reductions have been specific to squamous cell carcinoma (SCC) and have not included adenocarcinoma (AC). Incidence of AC has increased steadily over the last 20 years. The intent of this article is to examine trends in cervical adenocarcinoma incidence in Ontario over a 20-year period in relation to screening practices. All cases of cervical cancer between 1981 and 2002 were extracted from the Ontario Cancer Registry (a population-based, provincial-wide database). Age-standardized incidence rates were calculated overall, by broad age groups and by morphological type (SCC and AC). Time trends were assessed using JoinPoint methodology. In Ontario, opportunistic cervical cancer screening has been accompanied by significantly decreased rates of SCC since at least 1981. Conversely, the incidence of AC rose by 3.1% per year (95% CI: 1.6%, 4.6%) between 1981 and 1995, and subsequently declined by 4.0% per year (95% CI: 27.4%, 20.5%). From the mid-to late-1990s, instructions were distributed to clinicians, reinforcing the importance of dual specimen collection (i.e. using both spatula and endocervical brush). At the same time, laboratories routinely provided physicians with kits that included both spatula and brush. The subsequent decline in AC incidence may be due, in part, to improved specimen collection. As well, the decline may be partly due to increased awareness of AC precursors among cytopathologists and clinicians, and/or improvements in laboratory training and quality assurance. ' 2006 Wiley-Liss, Inc.