Objectives—To investigate the effect of cranial cruciate ligament (CrCL) insufficiency on morphology of the canine caudal cruciate ligament (CdCL).Study Design—In vivo experimental study.Animals—Five adult foxhounds.Methods—Two years after CrCL transection, the histologic appearance of CdCLs from CrCL‐deficient and unoperated contralateral control (CrCL‐intact) stifle joints were evaluated using light and transmission electron microscopy.Results—CdCLs from CrCL‐deficient joints had extracellular matrix changes, characterized by chondroid metaplasia and disruption of cell architecture. Percent of small‐diameter fibrils in CdCLs from CrCL‐deficient joints was significantly greater (P<.05) than that in CdCLs from CrCL‐intact joints. Collagen fibril density in CdCLs from CrCL‐deficient joints (41.09 ± 5.39%) tended to be less than that in CdCLs from CrCL‐intact joints (52.96 ± 6.92%); however, this difference was not significant (P= .056). Mean eccentricity (ratio of minor to major diameters) of collagen fibrils was significantly (P< .0001) lower for CdCLs from CrCL‐deficient joints (0.85 ± 0.016) when compared with that for CdCLs from CrCL‐intact joints (0.87 ± 0.015).Conclusions—Significant alterations were found in the morphology of CdCLs from CrCL‐deficient joints. These changes may be associated with repetitive microtrauma to the CdCL secondary to instability or enzymatic degradation in the hostile synovial environment of an unstable joint.Clinical Relevance—Regardless of the cause, the switch to a predominantly small‐diameter collagen fibril profile may reflect compromised material properties of the CdCL. This should be taken into account when considering surgical techniques that rely on the CdCL to stabilize CrCL‐deficient stifles.