OBJECTIVE Limbal dermoids usually involve corneal stroma and more rarely might extend into the anterior chamber. Depending on the size and amount of penetration of the lesion, different therapeutic approaches are indicated. Depth information is difficult to obtain by slit-lamp examination because the structure is opaque. We investigated the use of ultrasound biomicroscopic (UBM) examination for surgical planning in limbal dermoids. METHODS The UBM (Zeiss Humphrey) with its 50-MHz probe was used for preoperative evaluation of the depth of penetration in two cases of infantile limbal dermoid. Histology specimens of the lesion corresponding to the UBM images were obtained. RESULTS UBM was able to distinguish normal cornea from the more sonolucent lesion. Presence or absence of Descemet's membrane could be identified. Depth of involvement of limbal dermoids could be assessed. CONCLUSIONS UBM is able to assess depth involvement of opaque corneal lesions such as limbal dermoids. Because planning of the surgical approach in these cases is facilitated by preoperative knowledge about the depth of penetration of these opaque lesions, UBM can be regarded as a helpful tool in the clinical management.