Nine morphologic patterns of tumor vessels were identified in eyes removed for ciliary body or choroidal melanoma by the examination of tissue sections stained with fluorescein-conjugated Ulex europaeus I using laser scanning confocal microscopy. This technique also highlights intravascular tumor invasion. Each of these nine morphologic patterns of tumor vessels also may be demonstrated by a modification of the periodic acid-Schiff reaction, viewed with a green narrow band pass filter, but this modified histochemical technique does not accurately identify intravascular tumor invasion. Most tumors have a heterogeneous distribution of vascular patterns. Melanomas in two groups of 20 tumors each were matched by tumor size and location (one group of tumors from patients who survived at least 15 years free of metastatic melanoma after enucleation and one group of tumors from patients who died of metastatic melanoma). A matched case-control analysis indicates that the presence of at least one closed vascular loop in a uveal melanoma is the most significant vascular pattern associated with death from metastatic melanoma after enucleation. Closed loops are associated with other histologic features that are predictive of an unfavorable outcome after enucleation: epithelioid cells and mitotic figures. In this preliminary study the formation of closed vascular loops is a marker of tumor progression in ciliary body and choroidal melanomas.