The role of interleukin (IL)-23 in the pathogenesis of inflammatory bowel disease (IBD) remains unclear. The aim of this work was to study the serum level of IL-23 in IBD with and without arthritis and determine its relation to the subsets and clinical features of the disease. Thirty-seven patients with IBD including 11 with arthritis were included in the study with a mean age of 30.86 ± 4.66 years. Twenty healthy subjects served as control. Seronegative spondyloarthropathy was present in 11 (29.73 %) of the IBD patients; Crohn's disease (CD) was present in 23 and 14 had ulcerative colitis (UC). Serum level of IL-23 was measured in all patients and control by ELISA. IL-23 was significantly higher in IBD patients (46.24 ± 27.19 pg/ml) compared to control (24.1 ± 2.31 pg/ml) (p < 0.0001) being higher in CD patients (52.57 ± 32.78 pg/ml) compared to those with UC (35.86 ± 6.41 pg/ml) (p = 0.026). Furthermore, it was significantly higher in those with peripheral and/or axial arthritis (67.73 ± 40.85 pg/ml) compared to patients without (37.15 ± 10.37 pg/ml) (p = 0.03). There was a tendency to a higher level in males (49.15 ± 30.97 pg/ml) compared to females (38.4 ± 9.54 pg/ml). Serum IL-23 is increased in IBD especially those with CD associated with arthritis and sacroiliitis. The IL-23 could be added to the biomarkers of development of arthritis in IBD patients. These results also confirm the findings of previous studies on the critical role played by IL-23 in the pathogenesis of IBD making it an important new therapeutic target for these patients.