Objective: To evaluate the reliability of 3-dimensional ultrasound (3D-US) for the measurement of choroidal melanomas. Design: Retrospective case series. Participants: Forty-two consecutive cases of choroidal melanoma imaged with 3D-US. Methods: Tumor measurements obtained with ophthalmoscopy, transillumination, standard ultrasound techniques, 3D-US, and pathological studies. Tumor diameters, heights, and volumes were compared. Our 3D-US tumor measurement techniques were tested for intraobserver and interscan reproducibility. Results: Fifty 3D-US images were studied. The 3D-US tumor measurements were found to be reproducible (height coefficient of variation [CV] ≤3%; diameter CV ≤9.7%; volume CV ≤13.2%). There was significant correlation with the usual methods of tumor measurement (diameter r=0.76; height r≥0.98). Significant differences were found between measurements at pathological examination, as compared with both 2-dimensional and 3D-US height measurements (range, 0.73-0.83 mm). This finding was thought to be due to specimen shrinkage. Three-dimensional ultrasound was found to be at least as reproducible as clinical examination and standard ultrasound techniques used for measurement of diameter and height of choroidal melanomas. It was our impression that the 3D-US volume measurements accounted for the geometry of the tumor better than volume estimates calculated from basal area and tumor height. Conclusions: Three-dimensional ultrasound measurements of choroidal melanoma were reproducible, correlated well with other tumor measurement techniques, and can be used for measurement of choroidal melanomas.