Health care services in Catalonia (Spain) are organized in a national health service with universal population coverage and include preventive services such as mammography and Pap tests. In addition to a national health service (NHS) coverage, 22% of the population is enrolled in a voluntary private health insurance (VPHI), leading to a double coverage. This situation offers an opportunity to study the impact of this organizational aspect of health care with regard to cancer screening access. The source of data was the Catalan Health Survey (CHS), a cross-sectional survey conducted in a random sample of non-institutionalized population carried out in 1994. Variables analysed were age, educational level and voluntary private health insurance (VPHI). Women were asked if they had ever had a mammography and Pap test for preventive purposes. Logistic regression was used to study the relationship between these variables and the mammography or Pap test participation. The study sample was 5865 women aged 20 years and older. A Pap test and mammography were carried out on 42% and 25% of women, respectively. Participation had a peak between the ages of 30 and 39 years in Pap test and between 40 and 49 years in mammography; it decreased in older women. The percentage of Pap test practice increases according to a higher educational level than it does in mammography. Women who had a VPHI showed a higher percentage of screening tests than the rest of the population. There is also an increase in the mammography practice related to the educational level in older groups, but this fact is not observed in women younger than 40 years. Multivariate logistic regression analysis showed an increase in the likelihood of ever had a mammography and a Pap test according to age and to educational level, although this situation is less pronounced in older age groups. Both variables (educational level and age) remained significant after introducing the VPHI into the model (women who reported having a VPHI were more likely to have had a Pap test and a mammography than the rest of the women). In conclusion the opportunistic screening is associated with age, educational level and VPHI. Educational level is also associated with participation in both screening tests after adjusting by age. Furthermore, screening for cervical cancer shows a higher educational gradient than for breast cancer screening. The influence of VPHI after adjusting by age and by educational level poses the question about the role of private health insurances with regard to preventive practices in the context of a national health service aimed at promoting equity of health care access.