BACKGROUND: The aim of this study is to provide a valid and reliable German version of the Tegner activity scale (Tegner-G). The Tegner activity scale assesses on 11 levels the activity in sports (competitive and recreational) and work of patients with anterior cruciate ligament injuries. The English original version was elaborated in Sweden and contains sports that are unknown in German-speaking countries. METHODS: The translation and adaptation was conducted in several steps according to the guidelines in the literature. The validity (discriminative validity and content validity) and (absolute and relative) reliability were determined in 46 patients after reconstruction of the anterior cruciate ligament and in 20 healthy subjects. The patients were divided into an acute group (< 3 months after operation; 11 men; 30.9 ± 8.3 years) and a chronic group (3 - 12 months after operation; 18 men; 31.3 ± 11.6 years). All subjects filled in the scale two times within 3 - 7 days. For the additional determination of the relation between activity and function, they also filled in the German version of the Lysholm score (Lysholm-G). RESULTS: The three groups differed significantly from each other (Kruskal-Wallis test: χ2 = 27.95, p < 0.001; post hoc Mann-Whitney U tests: acute-chronic p < 0.001; acute-control p < 0.001; chronic-control p = 0.003). There was a floor effect in the acute patient group. The intraclass correlation coefficients indicated a high relative reliability (ICC2,1 > 0.9). The minimal detectable change was 1.4 points. The relation between activity (Tegner-G) and function (Lysholm-G) was stronger in the acute than in the chronic patient group (ρ = 0.77 and ρ = 0.60, respectively). CONCLUSION: The psychometric properties of the Tegner-G are comparable to those of the English original version. The Tegner-G is thus valid and reliable for the German-speaking part of Switzerland. The application in other German-speaking countries probably requires adaptations for some of the sports included. The relation between activity and function changes depending on time since operation. This confirms that a comprehensive assessment of the outcome after an anterior cruciate ligament injury requires the separate assessment of both parameters.