Glaucoma is a leading cause of irreversible vision loss. Mental health and quality of life (QoL) are important issues for patients with glaucoma because visual impairment can be related to those. Analysis of mental health status or QoL in undiagnosed glaucoma patients can be free of the bias caused by awareness of the disease itself. In this study, the association between mental health status or QoL and undiagnosed glaucoma, along with the effects of visual acuity or visual field damage was investigated. Among individuals in the Korea National Health and Nutrition Examination Survey (KNHANES) V (2010–2012), subjects 40 years or older were included. KNHANES is a cross-sectional study using a stratified, multistage, probability sampling survey. The KNHANES includes questionnaires to assess psychological health, including depression, sleep duration, psychological stress, and suicidal ideations. To evaluate QoL, the KNHANES includes the EuroQoL, which is composed of a health-status descriptive system (EuroQol 5-dimension, EQ-5D) and the EQ visual analog scale (EQ-VAS). The proportion of people reporting symptoms of “some or severe problems” in all 5 dimensions of the EuroQoL-5 instrument, including anxiety/depression, was higher in the glaucoma group than in the nonglaucoma group. The subjective health status reported by the EQ-VAS was lower in the subjects with glaucoma than in those without glaucoma. Suicidal ideation was greater in subjects with glaucoma than in those without glaucoma (P = 0.005). After adjustment for demographic factors, glaucoma subjects were more likely than those without glaucoma to have some or severe problems with anxiety/depression (odds ratio 1.77; 95% confidence interval, 1.26–2.49). Worse best corrected visual acuity was associated with more problems with a lower EQ-5D score in glaucoma subjects. Individuals who had undiagnosed glaucoma were more depressed than those without glaucoma. QoL can be affected by glaucoma, especially in patients with worse visual acuity.