It is difficult to classify lesions of the iris, especially when they are posterior or in the iridociliary angle of the eye.We used an ultrasound biomicroscope (Humphrey, Zeiss, Oberkochen, Germany) with a high-frequency sound head (30 and 50 Hz). This study included all patients with unspecified iris processes who were examined at the University Eye Clinic and Hospital of Ulm between September 1996 and February 1997. Fifteen patients, aged between 9 to 82 years (average age = 48.9 years), were prospectively evaluated.A cyst of the iris or ciliary body causing a tumor of the iris was found in six cases (40%). Seven patients (47%) showed a solid tumor of the iris and two patients (13%) a solid tumor of the ciliary body.The ultrasound biomicroscope can be used to assess lesions of the iris caused by a cyst or a solid tumor. The increasing size and depth expansion of a solid tumor may be helpful for differentiating between a malignant or benign process. Up to now it has not been possible to use the ultrasonic reflectivity of the tumor to decide if it is malignant.