Purpose: To examine the long-term risk of glaucoma after cataract surgery in childhood. Methods: This study took place from January 2022 until December 2022 and included patients from a large family with hereditary childhood cataract who had cataract surgery before 18 years of age. Patients underwent an ophthalmologic examination to determine the presence of glaucoma or ocular hypertension (OHT). Patients who did not want to participate in the examination could contribute with a medical journal from their treating ophthalmologist. The risk of long-term glaucoma was determined using survival analysis, and risk factors were assessed using a Cox proportional hazards regression model. Results: We included 68 patients (133 eyes) with a median age at cataract surgery of 7 years (IQR: 5–10). The median follow-up time after cataract surgery to glaucoma/OHT or the latest ophthalmologic examination was 35 years (IQR: 15–48). Twelve patients (18 eyes) had glaucoma, and five patients (eight eyes) had OHT, resulting in 15 patients with glaucoma/OHT. The long-term risk of glaucoma/OHT diagnosed in adulthood was 47.7% (CI: 21.8–70.9) at the age of 70 years of patients who were free of glaucoma before their 18th year. We could not confirm or dismiss an association between glaucoma/OHT and sex, age at surgery, number of ocular interventions before 18 years of age or glaucoma after cataract surgery in a first-degree relative. Conclusion: Cataract surgery in childhood is associated with a high risk of late-onset glaucoma. Regular lifelong follow-up is important to ensure early diagnosis and prevent extensive vision loss.