The purpose of this study was to examine the pathological changes in the Achilles tendon and its paratenon after intratendinous corticosteroid injections and to reveal the effects of this drug on healthy tendon. We also sought for the effects of these injections compared with compression with a clamp on the Achilles tendons of the rats. Fifty-two Achilles tendons in 26 male Wistar rats were included in the study. Betamethasone injections were applied to the left tendons at different intervals, while the right tendons served for compression with mosquito clamps for varied periods. At the end of 30 days, all of the tendons were excised and examined histopathologically according to a semiquantitative scoring system. Histopathologic evaluation demonstrated some degree of degeneration in both groups. Statistical analysis showed no significant difference among the two groups, but in macroscopic evaluation, the tendons in the betamethasone group demonstrated enlargement and strong adhesion to the subcutaneous tissue. We conclude that intratendinous betamethasone injections are as harmful as compression with a clamp and can be used as a degeneration-producing model in further studies. Enlargement of the tendon mass and strong adhesion to the subcutaneous tissue can be due to injection of the betamethasone partly outside the tendon.