Forty-two (16%) of 261 patients with ocular melanoma who were treated with helium ions between January 1978 and November 1986 have developed metastatic disease. The time between start of helium ion treatment and recognition of metastatic disease ranged from 3 to 67 months (median, 27 months). The mean pretreatment tumor height in the patients with metastases was 7.7 mm. All 42 patients who developed metastatic disease have died. The median survival after diagnosis of metastatic disease was 5 months; the longest survival was 49 months. The most common site of metastasis was the liver (n = 34). Four (10%) of the 42 patients with metastases also had local recurrence of the tumor. Multivariate analysis identified three variables that predicted independently the development of metastases and lack of survival. These variables are anterior location of tumor (P = .027), tumor height greater than 5 mm (P = .02), and tumor diameter greater than 10 mm (P = .0075).