Background: It is unknown if genetics contribute to the etiology of acute Achilles tendon rupture (ATR). The aims of the present study were, 1) To calculate the concordance rate for monozygotic (MZ) twins and same-sex dizygotic (SSDZ) twins and 2) to estimate the heritability of ATR. Methods: The study was performed as a registry study using the Danish Twin Registry and the Danish National Patient Registry. Results: The study sample consisted of 85,534 twins born from 1895 to 1995. Of these, 572 (0.67%) were registered with ATR in the period from 1994 to 2014. The concordance rate was 8.1% (95% CI 1.4–14.7%) for MZ twins and 4.3% (95% CI 0.7–7.9%) for SSDZ twins. The heritability of ATR was 47% (95% CI 31–62%). Conclusion: This study found that genetics contribute substantially to the etiology of ATR with an estimated heritability of the liability to ATR of approximately 50%. The finding generates the hypothesis that genetics play a role in the pathological changes that occur in the Achilles tendon before a rupture. The risk of ATR for a twin within a 20 year period, if the co-twin has had an ATR, was 8% for MZ twins and 4% for SSDZ twins.