The public perception of ultimate disposal facilities for Radioactive Waste (RW) and carbon dioxide (CO2) is crucial for the selection, construction and operation of such sites. This paper presents a cross-national comparison of the public perceptions of ultimate disposal facilities for RW and CO2 in the Czech Republic, Germany and Lithuania. The results of the comparison revealed similarities and differences in public perceptions in the three countries, as well as similarities and differences in the public perception of the two issues of RW and CO2 disposal. Key lessons learnt from the comparisons are that (a) public knowledge about RW and CO2 disposal is still low, (b) misconceptions about RW and CO2 disposal are widespread, (c) risk perceptions of CO2 disposal sites among the public might be influenced by risk perceptions of RW disposal sites and (d) the social context of public perceptions should be taken into account.