Background Postoperative ascites (POA) is the most common complication after liver surgery for hepatocarcinoma (HCC), but its impact on survival is not reported. The aim of the study is to investigate its impact on overall survival (OS) and disease-free survival (DFS), and secondarily to identify the factors that may predict the occurrence. Method Data were collected from 23 centers participating in the Italian Surgical HCC Register (HE.RC.O.LE.S. Group) between 2008 and 2018. POA was defined as ≥500 ml of ascites in the drainage after surgery. Survival analysis was conducted by the Kaplan Meier method. Risk adjustment analysis was conducted by Cox regression to investigate the risk factors for mortality and recurrence. Results Among 2144 patients resected for HCC, 1871(88.5%) patients did not experience POA while 243(11.5%) had the complication. Median OS for NO-POA group was not reached, while it was 50 months (95%CI = 41–71) for those with POA ( p < 0.001). POA independently increased the risk of mortality (HR = 1.696, 95%CI = 1.352–2.129, p < 0.001). Relapse risk after surgery was not predicted by the occurrence of POA. Presence of varices (OR = 2.562, 95%CI = 0.921–1.822, p < 0.001) and bilobar disease (OR = 1.940, 95%CI = 0.921–1.822, p : 0.004) were predictors of POA, while laparoscopic surgery was protective (OR = 0.445, 95%CI = 0.295–0.668, p < 0.001). Ninety-day mortality was higher in the POA group (9.1% vs 1.9% in NO-POA group, p < 0.001). Conclusion The occurrence of POA after surgery for HCC strongly increases the risk of long-term mortality and its occurrence is relatively frequent. More efforts in surgical planning should be made to limit its occurrence.