The purpose of the study was to analyse, whether the shape and the height to base ratio in B-scan ultrasonography are appropriate to differentiate choroidal melanomas from metastases.Between 1991 and 1996 16 eyes of 16 patients with choroidal metastases from breast carcinomas and 66 eyes of 66 patients with choroidal melanomas were evaluated ultrasonographically. The diagnosis of choroidal melanoma has been confirmed histologically in all eyes. Irradiated tumours were excluded from the study. Fisher's exact test and chi 2 test were used for statistical analysis.Choroidal metastases demonstrated a significantly lower height to base ratio in B-scan (mean 0.18, SD 0.08) than melanomas (mean 0.6 (0.16); p < 0.001). A polygonal tumour surface was significantly more frequent in metastases (13 out of 16 metastases and in six out of 66 melanomas, p < 0.001). A choroidal excavation could be demonstrated in 38 melanomas and in no metastatic tumour (p < 0.001). The reflectivity was significantly higher in metastases than in melanomas.The combined use of height to base ratio and reflectivity enables a highly significant discrimination between choroidal melanomas and metastases from the breast, thus probably constituting appropriate variables for the clinical differentiation.