BACKGROUND: The sacroiliac joint (SIJ) is a common source of chronic low back pain. Published cohorts have reported favorable outcomes after SIJ fusion. We report the 12-month follow-up from SIJ fusion of the so far largest single-center and single-surgeon group. METHODS: Over 15,000 outpatients were evaluated for chronic low back and leg pain, of whom 3,477 underwent SIJ blocks. 541 patients were stringently selected to undergo SIJ fusion with triangular titanium implants (TTI). 483 patients had a follow-up of 12 months. Patients were seen every 3 months and completed visual analog scale (VAS) and Oswestry Disability Index (ODI) ratings. RESULTS: Mean age of all patients was 61 years, and the majority (65%) were women. 44% had undergone prior lumbar fusion and 10% had a spinal cord stimulator (SCS) in place at the time of SIJ surgery. 26% underwent non-simultaneous bilateral SI joint fusion. At 12 months, the proportion of patients with clinically important improvements in pain (≥ 2 points) was very high (100%). The proportion with substantial improvement (≥ 4 points) was 98%. Similarly, improvement in ODI was high, with nearly 99% having an improvement of ≥ 15 points by month 12. The proportions of patients with VAS ≤ 2 or ODI ≤ 15 was also high (92.8% and 48.9%). CONCLUSIONS: In our clinical practice, SIJ fusion with TTI produces significant improvement in pain and disability. The most important factor for achieving these clinical results may be the very stringent multistep selection of patients for surgery, which is described in detail, as well as the highly standardized and streamlined surgical procedure and the particular postoperative management.