Background In this study, we evaluated hepatobiliary involvement in inflammatory bowel disease (IBD) with FibroScan® (transient elastography) and examined drug effects on liver fibrosis and steatosis. We particularly focused on the effect of azathioprine (AZT) on spleen stiffness (SS). Methods A total of 352 subjects were included in this study, including 298 IBD patients and 54 healthy controls. LSM (liver stiffness measurement), SS, and CAP™ (controlled attenuation parameter) scores were measured by FibroScan®. In addition to disease and patient characteristics; laboratory tests, and effect of the drugs were evaluated and compared within the groups. Results The patient and control groups were similar in terms of age and gender. The characteristics of the groups are shown in Table 1. Mean LSM (5.2±3.1kPa vs 4.5±1,1kPa), mean SS (22.69±13,10kPa vs 17.96±7,44kPa), CAP™ score (hepatosteatosis) (233±56dB/m vs 224±47dB/m) were significantly higher in the patients with IBD than in the control group (p<0.05). Liver fibrosis and steatosis grades are shown in Figure 1. A positive correlation was found between CAP™ score and male gender, hypertension, diabetes, BMI, smoking, penetrating disease, GGT, triglyceride, LSM, and SS (p<0.05). LSM (5.7±3,1kPa vs 5.0±3,1kPa) was significantly higher in patients with extraintestinal involvement (p<0.05). In patients with significant liver fibrosis (F2-3-4), the frequency of anti-TNF treatment was lower (44,4% vs 69,5%; p=0,008) (Figure 2). In patients who use alcohol regularly compared to nondrinkers (25.54±14,83kPa vs 21.05±11,24kPa) SS was significantly higher (p<0.05). Additionally, in patients using AZT≥100 mg/day compared to those using AZT<100 mg/day (23.48±14,61kPa vs 19.99±11,84kPa; p<0,05) SS was significantly higher (Figure 3). AZT dose was positively correlated with SS (Spearman analysis; r=0.182 and p=0.013); however, no correlation was found with the duration or cumulative dose of AZT. The mean level of platelets was significantly higher in patients with IBD than in controls (300±104x10³/µL vs 251±52x10³/µL, p=0,001); however, there was no correlation between SS and trombosit level (p>0,05). 83% of patients were in clinical remission (Mayo score≤2/CDAI<150). No positive correlation was found between disease activity and SS in IBD patients. AZT-associated non-cirrhotic portal hypertension was detected in only one patient. Conclusion In this study, fatty liver, liver fibrosis, and SS were found to be significantly higher in IBD patients than in healthy controls. Although there is no relationship with the duration of AZT therapy, AZT dose was positively correlated with SS. We recommend that spleen stiffness should be evaluated in patients who use high doses of AZT (≥100 mg/day).