Introduction: Extracorporeal shock waves (ESW) have been extensively studied in the field of orthopedics. Experimental and focused, well-designed clinical studies have suggested the clinical utilisation of ESW in several pathologies including delayed bone union, tennis elbow, and plantar fasciitis. However, the unwanted detrimental effects of ESW on various tissues have been questioned by some authors. In this experimental study, the effects of ESW were investigated at different intensity applications on the Achilles tendons of rat. Materials and methods: A total of 32 adult Wistar albino rats was divided into four groups. The first three groups received 1000 impulses of 0.15 MJ/mm(2) 1500 impulses of 0.15 mJ/mm(2), and 2000 impulses of 0.20 mJ/mm(2), respectively. The last group was kept as the control group. Subsequently, Achilles tendons were harvested for histological studies from all rats at the 3rd week after a single application of ESW. Results: There were no histological abnormalities observed in the Achilles tendons of the first two groups compared with the control group. No alteration in the histological configuration was observed, and consequently the pathologist who had been blinded could not differentiate these rats from the control group by light microscopy. However, in the high intensity group (2000 impulses of 0.20 mJ/mm(2)), grade II and III disorganisation of collagen fibers was noticed in 7 out of 8 rats, which was not detected in any of the rats from the first two groups (p<0.05). Consequently, the pathologist could distinguish the majority of the rats (7 out of 8) of this group from the remaining ones. Meanwhile, grade I lymphocyte infiltration was observed in some sections of the rats receiving the highest ESW dose. Conclusion: This study confirms that ESW application at high intensity is associated with detrimental tissue effects. Additionally, it was suggested that the extent of tissue injury caused by ESW is dose-related.