Purpose: The aim of the study was to evaluate patient tolerability and compliance to two bowel cleansing agents (PEG-ELS and NaP) as well as to compare the cost effectiveness. Methods: Three hundred and forty-three consecutive patients were randomized to receive either the standard 4 l of polyethylene glycol and electrolyte lavage solution (PEG-ELS) or 90 ml of sodium phosphate (NaP). All patients were advised to be on a clear liquid diet one day before starting the bowel cleansing regimen and to take ornidazole orally (3 × 2 tablets) 24 hours before surgery. Patient tolerabilty and compliance to the regimens were assessed based on complaints of nausea, vomiting and the need of antiemetics. In addition completion of the regimens was evaluated in both groups. Results: The need for antiemetics because of nausea and vomiting was statistically higher in the PEG-ELS group than the NaP group (p = 0.000). Regimen completion rate was statistically higher in the NaP group than in the PEG-ELS group (p = 0.000). NaP is more cost effective than PEG-ELS. Conclusion: NaP was rated superior to PEG-ELS in terms of patient tolerability, compliance, completion of the regimen and cost effectiveness and should be the first-choice treatment.