Objective To assess whether preoperative gonioscopy status is associated with the development of postoperative glaucoma after phacoemulsification. Procedure Eligible dogs and eyes were selected from medical records (2007‐2017), and each eye was classified as having normal or abnormal gonioscopy status. Records were examined for postoperative glaucoma, and data were collected for baseline variables including patient signalment, surgical factors, and pre, intra, and postoperative medications. Results Of 305 dogs (505 eyes) selected for review in this study, 111 dogs (163 eyes) had abnormal gonioscopy findings, and 194 dogs (342 eyes) had normal gonioscopy findings. Postoperative glaucoma occurred in 24% (39/163) of eyes with abnormal gonioscopy and in 14% (49/342) eyes with normal gonioscopy. Eyes with abnormal gonioscopy status were at higher risk of postoperative glaucoma compared to normal eyes (P = .025). There was no important confounding due to the numerous baseline variables summarised above. Regardless of gonioscopy status, the risk of glaucoma was highest during the first 2 months after surgery. Conclusions Eyes with abnormal gonioscopy findings are at increased risk of postoperative glaucoma compared with eyes with normal gonioscopy findings. Gonioscopy is recommended as a part of presurgical assessment in all dogs prior to phacoemulsification. Further study is needed to assess whether the incidence of postoperative glaucoma can be reduced by increased monitoring or altered treatment protocols in cases that are known to have abnormal gonioscopy findings prior to cataract surgery.