To investigate if actual knowledge of Down syndrome (DS), influences the decision to accept or decline prenatal diagnosis (PND). Secondary aims were to elucidate reasons for accepting or declining PND and investigate differences between the accepting and declining group in perceived information, knowing someone with DS and thoughts about decision-making. A questionnaire was completed by 76 pregnant women who underwent invasive testing and 65 women who declined tests for chromosomal aberrations in Uppsala, Sweden. Apart from one question no significant differences were found in knowledge of DS between women declining or accepting PND for DS. Both groups had varying and in several respects low levels of knowledge about DS and its consequences. Most common reasons to accept PND were ‘to ease my worries’ and ‘to do all possible tests to make sure the baby is healthy’. Corresponding statements declining PND were ‘termination of pregnancy is not an option’ and ‘because invasive tests increase the risk of miscarriage’. More women declining PND knew someone with DS. Knowledge of DS at these levels is not a major factor when women decide to accept or decline PND for DS. Their choice is mostly based on opinions and moral values.