We prospectively studied 51 patients with choroidal melanomas in a masked manner to determine the accuracy of clinical, ultrasound, and fluorescein diagnosis as well as the accuracy of tumor size measurements. In patients with clear media, clinical diagnosis was the most accurate means of detecting a choroidal melanoma. There was excellent correlation between clinical, ultrasound, and pathology measurements of tumor size. In small melanomas, clinical examination was the most accurate means of measuring tumor diameter and ultrasound the most accurate method of measuring tumor height. Even with a trained ocular oncologist, there was a significant variability in tumor measurements on serial ophthalmoscopic examinations.