Measurement of the largest basal dimension (LBD) of intraocular tumors is important as a prognostic parameter. To evaluate the potential value of true color ultra-widefield fundus photography for measuring tumors, we compared LBD measurements of choroidal and retinal tumors using a color ultra-widefield fundus camera with clinical estimation based on indirect ophthalmoscopy and standardized ophthalmic ultrasound.The LBD of 148 choroidal and retinal tumors in 148 patients seen at Tongren Hospital were measured using ultra-widefield fundus photography and compared with measurements obtained using B-scan ultrasonography and clinical estimates based on indirect ophthalmoscopy.Paired t-tests and Bland-Altman plots reveal that measurements from ultra-widefield fundus photographic images are not statistically different from clinical estimates and ultrasound measurements. The results also showed that, although not statistically significant, when the tumor boundary was clear, the height was < 3 mm, or the tumor was pigmented, measurement from ultra-widefield fundus photography tended to be greater than those obtained by ultrasound.The LBD measurement using ultra-widefield fundus photography correlated well with ultrasonography and clinical estimation and could be used as a reliable tool for measuring the LBD of choroidal and retinal tumors.© 2023. The Author(s).