OBJECTIVE Treatment indications in unruptured intracranial aneurysms (UIAs) are challenging because of the lack of prospective natural history studies without treatment selection and the decreasing incidence of aneurysm rupture. The purpose of this study was to test whether the population, hypertension, age, size of aneurysm, earlier aneurysm rupture, site of aneurysm (PHASES) score obtained from an individual-based meta-analysis could predict the long-term rupture risk of UIAs. METHODS The series included 142 patients of working age with UIAs diagnosed before 1979, when these were not treated but were followed up until the first rupture, death, or the last contact. PHASES scores were recorded for all patients by using the baseline variables and compared with the new treatment score obtained from a recent cohort, consisting of age, smoking status, and aneurysm size and location. RESULTS Of the 142 patients, 34 had an aneurysm rupture during a total follow-up of 3064 person-years. The median time between diagnosis and an aneurysm rupture was 10.6 years. The PHASES score at baseline was higher in those with an aneurysm rupture than in the others (5.3 ± 2.3 vs 4.2 ± 2.2, p = 0.012), and the difference relative to the new treatment score was 5.3 ± 2.4 versus 3.0 ± 2.2 (p < 0.001). The receiver operating characteristic curve of the PHASES score for predicting rupture showed a fair area under the curve (0.674, 95% CI 0.558–0.790) where the optimal cutoff point was obtained at ≥ 6 versus < 6 points for sensitivity (0.500) and specificity (0.811). The area under the curve of the new score was 0.755 (95% CI 0.657–0.853), with the optimal cutoff point at ≥ 5 versus < 5 points for sensitivity (0.607) and specificity (0.789). CONCLUSIONS The PHASES and the new scores predicted the long-term aneurysm rupture risk moderately well, with the latter, which also included smoking, being slightly better and easier in clinical practice. The findings suggest that treatment decisions about UIAs in patients of working age can be done with an improved cost-effectiveness.