In countries where cervical cancer screening programmes are conducted on an opportunistic basis, an active search for women at risk should be made to increase coverage. The objective of our study was to assess the effectiveness of three primary care interventions consisting of providing written, telephone and face-to-face information to increase screening participation among women over the age of 25 years. A randomized experimental study with only one post-test control group was conducted on women aged 25–70 years. A total of 1676 women were randomly distributed into four groups and the following interventions were implemented: written briefing; telephone briefing; an invitation to attend a group meeting and no briefing (control group). The women were evaluated 2 years after the intervention. The outcome variable was participation or nonparticipation in cervical cancer screening. It proved possible to interview a total of 1122 women. Among the groups, homogeneity was tested in terms of sociodemographic characteristics and health-related variables. Women who had undergone cytological testing in the 2 years preceding evaluation had a lower mean age (P<0.001) than women who had not done so (45.5±11.0 vs. 48.8±13.0 years). The proportion of women who had participated in screening was as follows: 35.3% in the written information group [95% confidence interval (CI) 29.8–40.9]; 38.4% in the telephone information group (95% CI 32.5–44.2); 29.3% in the face-to-face information group (95% CI 22.8–35.7) and 26.1% in the control group (95% CI 21.2–30.9), with this difference proving statistically significant (P=0.005). Logistic regression showed that only the interventions based on written or telephone briefing were effective vis-à-vis the control group. In conclusion, both written and telephone information can serve to improve women’s participation in opportunistic cervical cancer screening. Current preventive strategies could be optimized by means of simple interventions within the scope of health professionals.