Introduction: Improving the knowledge and attitudes of people facing an opioid overdose is one of the key prevention measures for reducing overdose occurrence and severity. In this respect, the Opioid Overdose Knowledge Scale (OOKS) and Opioid Overdose Attitudes Scale (OOAS) have been developed and validated in English to assess and improve knowledge and attitudes of opioid users and their families and care providers, in case of an overdose. Here, the OOKS and OOAS scales have been translated into French, Spanish, and German, and the different versions of the 2 scales have been assessed regarding their psychometric properties., Methods: The translation procedure of the scales was based on the international recommendations, including a back translation by a native English speaker. Subsequently, 80 (Spain: 29, France: 27, Germany: 24) former or current heroin users, aged from 20 to 61 years (M = 39.4 ± 9.23), completed the OOKS and OOAS versions of their native language, in test-retest, without specific between-assessment training. Internal consistency was assessed using Cronbach's α, while test-retest reliability was assessed using intraclass correlation coefficient (ICC). The correlation between the OOKS and OOAS scores of a same language was assessed using Spearman's (ρ) coefficient., Results: Internal consistency of the OOKS was found to be good to very good, with Cronbach's α ranging from 0.62 to 0.87. Test-retest reliability was also very good, with ICCs ranging from 0.71 to 0.82. However, results were less reliable for the OOAS, as internal consistency was questionable to acceptable, with Cronbach's α ranging from 0.12 to 0.63, while test-retest ICCs were very good for the French (0.91) and Spanish (0.99) versions and barely acceptable for the German version (0.41). No significant correlation was found between the OOKS and OOAS scores, irrespective of the version concerned., Conclusion: While satisfactory results were found for the 3 versions of the OOKS, results on the OOAS were relatively inconsistent, suggesting a possible gap between knowledge and attitudes on overdose among opioid users., (© 2021 S. Karger AG, Basel.)