A correct interpretation of the result of a CF carrier test and a correct understanding of the risk of having a CF child is complicated by the limited sensitivity of the DNA test. The present paper addresses this problem, with special attention for the residual risk after a negative test result. Secondly, the impact of the test results on child bearing decisions is evaluated. Seventy percent of a sample of 200 subjects tested in the Center for Human Genetics in Leuven answered a mailed questionnaire and participated in an interview. Knowledge about the recessive transmission of CF was weak. In the case of both partners receiving a negative test result, more than half the subjects were not aware of the restrictions of DNA testing, and were convinced that there was no residual risk. Two thirds of the subjects from the 'carrier + negative test result couples' were aware of the residual risk of having a CF child. This risk did not hamper further reproduction. Carriers who were single or whose partner was not tested, had much difficulties to understand the risk. Although most of them had no idea about their exact risk level, it influenced their childbearing decisions to some extent. It was also shown that the own risk of having a CF child had an impact on attitudes toward reproduction in hypothetical situations with different risk levels.