For a retrospective study, the researchers sought to determine the long-term clinical outcomes and the occurrence of iliac screw-related problems in patients with adult spinal deformity (ASD). The data of eligible ASD patients who had a spinopelvic fixation with bilateral iliac screws and had at least a 5-year follow-up time were evaluated retrospectively. Distal instability (DI) was characterized as iliac screw loosening and rod breakage between the S1 and iliac (S1/IL) screws. The DI group’s demographic data, health-related quality of life scores, and spinopelvic characteristics were compared to the non-DI group’s. Cases with and without alignment change after rod fracture at S1/IL were divided into sub-groups for analysis. The data of 110 patients (15 men, 95 women; mean age, 67.8 years) were evaluated out of 159 total. The percentage of follow-up was 69%. DI was found in 45 (41%) of the individuals (29 cases [26%] in screw loosening, 16 cases [15%] in rod breakage). Because of iliac screw-related problems, 8 patients (7.3%) underwent revision surgery. Between the DI and non-DI groups, no significant differences in Oswestry Disability Index and Scoliosis Research Society Questionnaire (updated) scores were found. Preoperative pelvic incidence, pelvic tilt (PT), postoperative PT, and T1-pelvic angle were all significantly higher in patients with iliac screw loosening. About 5 patients (31%) who had related mechanical difficulties with rod breakage at S1/IL demonstrated an alignment change between pre and after rod breakage. High-grade osteotomies and L5/S interbody fusion were found to be considerably higher and lower, respectively. The occurrence of iliac screw-related problems was quite high. They had little influence on sagittal alignment degradation, though, and only a few instances necessitated revision surgery.