The right not to disclose one’s belief or tenet, which is of particular importance in protecting the individual from oppressive interventions by authoritative regimes, was secured in the Constitution of 1982, and was introduced as a core right that could not be touched in state of emergency regimes. That said, the Constitutional Court concluded in decisions issued during the periods of Constitution of 1961 and the Constitution of 1982 that the inclusion of the religion box on identity cards did not violate the rights of the individual not to disclose one’s belief, despite the clear wording of the Constitution. However, in a recent case, the ECtHR found that the inclusion of the religion box on identity cards in Turkey violated the right to freedom of belief, stating that the right not to disclose one’s beliefs was protected by the right to freedom of belief. In this study, first, the development of the ECtHR case law on the right not to disclose one’s belief is examined, after which the decision of the Constitutional Court regarding the religion box on identity cards is discussed. Finally, the new national identity cards that have recently entered into use are assessed in terms of the right not to disclose one’s belief. Within the framework of this assessment, the case law amendment of the Constitutional Court with regard to the principle of secularism and its recent individual application decision on the right not to reveal one’s belief are also discussed.