The clinical implications of computed tomography (CT) detected sacroiliac joint (SIJ) changes compatible with sacroiliitis has been rarely discussed in the literature. The aim of the present study was to describe prevalence and clinical correlations of sacroiliitis, noted incidentally by abdominal CT in patients referred for non-musculoskeletal complaints, utilizing the New York radiological grading criteria for reference. Five hundred ninety-eight CT scans of the abdomen of patients 18–55 years old, performed at a community medical center, were prospectively examined for the presence of imaging changes consistent with sacroiliitis. Patients with the evidence of bilateral sacroiliitis of grade ≥2 were interviewed and underwent a rheumatologic examination. Twenty-two patients (13 females) were enrolled. Only eight patients (six males) had a history and clinical picture compatible with previously undiagnosed axial spondyloarthritis (SpA). Only the presence of erosions/joint space irregularity and/or inhomogeneous osseous sclerosis around SIJs on CT correlated with the clinical diagnosis of axial SpA. Dense homogenous osseous sclerosis was unrelated to axial SpA and was seen almost exclusively in females. The prevalence of incidental CT sacroiliitis is low, while the New York radiological grading criteria for diagnosing sacroiliitis may be inappropriate for CT imaging. CT noted erosions of the SIJ appear to be a reliable diagnostic sign of sacroiliitis, while the significance of the osseous sclerosis, seen on CT adjacent to SIJs requires better understanding.