BACKGROUND: Sacroiliitis following lumbosacral fixation is an important cause of postoperative low back pain and should be properly diagnosed and managed to improve the short- and long-term postoperative outcomes. OBJECT: We aimed to assess the prevalence of sacroiliitis following lumbar fusion procedures and the possible options of treatment available for such complication. METHODS: In this retrospective cross-sectional study, 100 patients who underwent spinal fusion surgery were included and observed for the next 3 months following surgery to detect postoperative sacroiliitis. RESULTS: One hundred patients aged 23- 65 years were included in the current study, with a mean age of 43.1±5.7 years. Fifty seven percent were females and 43% were males. Forty-seven patients (47%), 22 females (46.8%) and 25 males (53.2%), experienced sacroiliitis after a duration of 23.7 to 71 days post-operative with a mean of 33.8±1.7 days post-operative. Muscle relaxants and non-steroidal anti-inflammatory drugs (NSAID) were prescribed to all patients; 26 out of 47 patients (55%) responded well to medical treatment for 28 days with reduction of pain visual analogue scale (PVAS) from 7.3±2.1 to 3.3±1.4. In 21 patients (45%), medical treatment failed and physiotherapy sessions were added to medical treatment for 28 days with improvement of PVAS from 6.5±1 after 28 days medical treatment to 2.9±1.9 after medical treatment plus physiotherapy sessions. Five patients needed intra-articular steroid injection with further improvement of PVAS to <1. CONCLUSION: Sacroiliitis is an important cause of low back pain post lumbar fixation. Sacroiliitis is a frequent complication after lumbar fusion surgery detected in 47% of our study group. It was successfully managed with NSAIDs and physiotherapy in most of the cases.