To report a family with a myocilin (MYOC) gene mutation ascertained on the basis of the phenotype of the 71-year-old proband with juvenile-onset primary open-angle glaucoma (JOAG).A thorough patient history of the proband and review of medical records revealed that a filtering procedure performed 50 years before had controlled the intraocular pressure (IOP) and prevented optic disc damage and visual field loss until the bleb failed after cataract surgery. Patient characteristics and history led to suspicion of a mutation in the MYOC gene. Mutation screening and clinical evaluation of the proband and family members were undertaken.A Val426Phe mutation was found in the JOAG proband and in 3 other blood relatives with glaucoma. The mutation was not present in unaffected relatives.A functioning filtering procedure performed 50 years before the current study was all that was needed to prevent glaucomatous damage and control IOP in the proband. Once the bleb failed, increased IOP led to damage in a relatively brief period of time. Although not every JOAG patient has the MYOC mutation, there is a somewhat typical MYOC phenotype that may predict an increased chance of harboring a MYOC mutation. Use of such phenotype information in evaluating whether to screen older patients can lead to identification of families at risk for open-angle glaucoma.