Sacroiliitis is the inflammation of the sacroiliac joint and it can occur due to a great number of reasons. The reasons for the sacroiliitis can be divided into two groups: non-infectious (inflammatory) and infectious causes. Sacroiliitis is seen because of non-infectious causes generally. Non-infectious causes include spondyloarthropathies (such as ankylosing spondylitis), certain medications, various oncological conditions, pregnancy, and trauma, with ankylosing spondylitis being the most common [1]. But this inflammation may be a result of some infectious conditions rarely. When it comes to infectious etiologies, tuberculosis and brucellosis are the most common infections causing sacroiliitis [2]. Because infectious etiologies of the sacroiliitis are seen rarely, making a diagnosis of these reasons may be difficult. These infectious/rare reasons for sacroiliitis should be also taken into account in the differential diagnosis. It may be challenging to make the diagnosis of sacroiliitis because its clinical presentation can be similar to several other conditions such as lumbar disc herniation, sciatica, and some hip pathologies. In this instance, a detailed anamnesis, a comprehensive physical examination, and required imaging modalities might help to make the correct diagnosis and to determine the etiology. Determining the etiology is extremely pivotal because the treatment options of sacroiliitis are put forth according to the underlying etiology. Septic sacroiliitis is one of these infection-associated causes and might give rise to severe complications if remained untreated. Although the mentioned infectious causes are already rare, septic sacroiliitis is extremely rare with a prevalence of % 1 among cases of sacroiliitis in adults [3]. Septic sacroiliitis is seen because of infectious microorganisms such as Mycobacterium tuberculosis, Brucella spp., Streptococcus spp., and Staphylococcus aureus [4]. Early diagnosis and treatment of septic sacroiliitis are quite important to avoid possible unexpected/severe complications. Cases of septic sacroiliitis have been reported in the current literature so far [2] but to the best of our knowledge, a case report of a septic sacroiliitis complicated with abscess and caused by Staphylococcus xylosus has not been reported until now. In the pertinent literature, there are several cases in which Staphylococcus xylosus was described as the causative agent. Staphylococcus xylosus was previously isolated from brain abscess [5] and pancreatic pseudocyst [6] but was not isolated in a septic sacroiliitis case. This case report aims to highlight that septic sacroiliitis can be seen due to a unique/previously unknown causative agent (in our case, it is Staphylococcus xylosus) and this possibility should be kept in mind. We claimed that this is the first septic sacroiliitis case caused by Staphylococcus xylosus and we wanted to make a valuable contribution to the medical literature with this case presentation. In this case presentation, our aim was two-fold. First, we aimed to emphasize that septic sacroiliitis is rare, its accurate diagnosis can be challenging but early diagnosis and treatment are crucial. Second, we also wanted to report this case which has distinguishing features like the existance of abscess and the type of microorganism isolated from abscess culture.