BACKGROUND There are cases in which intractable pleural effusion and/or ascites appear even in the non-cirrhotic liver following extended liver resection, making postoperative management difficult. In this study we investigated the risk factors for pleural effusion and ascites following extended hepatectomy. METHODS Subjects were 50 patients between 1996 and 2003 who had hepatic metastasis of colorectal cancer, and who underwent extended liver resection of hemihepatectomy or greater at a time separate from the surgery for their colorectal cancer. The 50 patients were classified according to the presence or absence of pleural effusion and/or ascites, and compared for preoperative ICGR15, pre- and postoperative total serum protein and albumin levels, operating time, amount of blood loss, resected liver weight g/bodyweight kg (Hx ratio), intraoperative fluid replacement volume, period of surgery, operative procedure, use of serum and plasma derivatives, and use of catecholamines. RESULTS In a univariate analysis of pleural effusion and ascites, the Hx ratio, period of surgery, operative procedure, use of fresh frozen plasma and use of albumin preparations were significant factors, but in a multivariate analysis only the Hx ratio was a significant independent factor. Among patients with an Hx ratio of 8 or above, many had postoperative pleural effusion and ascites. CONCLUSIONS The Hx ratio is a simple method for the evaluation of postoperative remnant liver function and is extremely useful as a predictive factor for pleural effusion and ascites following extended hepatectomy in the non-cirrhotic liver.