Left ventricular thrombosis and systemic emboli have been demonstrated to complicate cardiomyopathy in Duchenne and Becker muscular dystrophy (DMD, BMD). We investigated plasma levels of pro-thrombin fragment 1+2 (F1+2), thrombin-antithrombin III complex (TAT) and circulating levels of tumor necrosis factor-α (TNF-α), a pro-coagulant cytokine that has been shown to be elevated in patients with depressed cardiac function, in 20 patients with DMD and 12 patients with BMD as compared with 30 age-matched control subjects. Significantly elevated levels of F1+2 (DMD: 1.4 ± 0.8 nmol/l; BMD: 1.8 ± 0.8 nmol/l vs. controls: 0.7 ± 0.2 nmol/l, p <0.01 and p <0.001, respectively), TAT complexes (DMD: 4.7 ± 2.7 αg/l, BMD: 5 ± 2.3 αg/l vs. controls: 1.6 ± 0.5 αg/l, p <0.001) and TNF-α (54 ± 9 vs. 25 ± 7 pg/ml, p <0.001) were observed in patients with the dystrophic disease compared to control subjects. A significantly negative correlation was also found between F1+2 and TAT complexes and left ventricular ejection fraction (r = –0.65, p <0.0001; r = –0.80, p <0.0001, respectively) and a positive correlation between F1+2 and TAT complexes and serum TNF-α levels (r = 0.67, p <0.0001; r = 0.70, p <0.0001, respectively). Our results indicate a hypercoagulable state in X-linked dystrophic patients. A possible relationship between haemostatic activation, left ventricular dysfunction and TNF-α system upregulation may be suggested.