High-frequency ultrasound biomicroscopy (UBM) has extensive powers of resolution. This makes it possible to explore and study some areas of the anterior segment with a clarity close to that of histologic preparations. High-frequency UBM was used in the clinical evaluation of 10 glaucomatous eyes subjected to ab externo holmium:yttrium-aluminum-garnet (Ho:YAG) laser sclerostomy. The anatomic characteristics of the fistular paths were viewed and compared with echographic images. The authors demonstrated that in the 5 cases where the filtering bleb, fistular path, and internal ostium were present, there was a reduction of intraocular pressure. UBM is a high-definition diagnostic instrument in the follow-up of fistular paths and filtering blebs after Ho:YAG laser sclerostomy, making it possible to reoperate at an early stage before the onset of clinical manifestations.