Abstract Background Adhesive small bowel obstructions are the most common postoperative causes of hospitalization. Several studies investigated the diagnostic and therapeutic role of water-soluble contrast agent (WSCA) in predicting the need for surgery, but there is no consensus. Methods A systematic review and meta-analysis was done of studies on diagnostic and therapeutic role of oral WSCA. Results WSCA had a sensitivity of 92% and a specificity of 93% in predicting resolution of obstruction without surgery; diagnostic accuracy increased significantly if abdominal X-rays were taken after 8 hours. The administration of oral WSCA reduced the need for surgery (odds ratio .55, P = .003), length of stay (weighted mean difference −2.18 days, P < .00001), and time to resolution (weighted mean difference −28.25 hours, P < .00001). No differences in terms of morbidity or mortality were recorded. Conclusions The administration of WSCA is accurate in predicting the need for surgery; the test should be taken after at least 8 hours from administration. WSCA is a proven safe and effective treatment, correlated with a significant reduction in the need for surgery and in the length of hospital stay.