Abstract Background Discrepancies between severity of lesions and symptoms may be observed in Crohn's disease. We prospectively assessed whether Crohn's disease may be diagnosed among asymptomatic relatives of patients, using Small Bowel Contrast Ultrasonography. Methods Diagnosis of asymptomatic Crohn's disease relatives was defined ultrasonographically as: bowel wall thickness >3mm, bowel dilation/stricture, lumen diameter >2.5cm. Diagnosis was confirmed by ileocolonoscopy. Subjects were also screened for the Leu3020insC mutation. Results Consent was given by 35 asymptomatic first-degree relatives of 18 Crohn's disease patients. Ultrasonography indicated increased bowel wall thickness (5mm) compatible with ileal Crohn's disease in 1 relative (2.8%), a 42 year-old male. Ileocolonoscopy, histology, and radiology confirmed the diagnosis of stricturing ileal Crohn's disease. Gallbladder stones were detected in 7/35 (20%) relatives and Leu3020insC mutation in 3/35 (8.5%). Conclusions Small Bowel Contrast Ultrasonography may be a useful tool to diagnose asymptomatic small bowel Crohn's disease among first-degree relatives of patients.