Background Our study validated the low anterior resection syndrome (LARS) score questionnaire, the colorectal functional outcome (COREFO) questionnaire, and the Memorial Sloan-Kettering Cancer Center bowel function instrument (MSKCC-BFI) in Greek rectal cancer patients. Methods Internal consistency, repeatability, construct and discriminant validity were evaluated for LARS, COREFO, and MSKCC-BFI questionnaires. The convergent validity was assessed by correlations with the European Organization for Research and Treatment of Cancer (EORTC) QLQ-C30 and QLQ-CR29 domains. Results The internal consistency of the questionnaire’s subscales was satisfactory (Cronbach’s a>0.6). The repeatability test showed extremely high reproducibility (intraclass correlation coefficient >0.9). High positive correlation was detected between the 3 questionnaires’ total scores and each of their questions (rho>0.5), indicating their valid construction. All questionnaires demonstrated a good convergent validity through correlations with comparable domains of the EORTC QLQ-C30 and CR29. Statistically significant associations were detected between LARS, COREFO, MSKCC-BFI scores and tumor distance and temporary stoma (P<0.001 and P=0.009, P<0.001 and P=0.005, P<0.001 and P=0.002 respectively). In addition, COREFO and MSKCC-BFI scores were significantly associated with radiation therapy. LARS score was significantly correlated to all COREFO and MSKCC-BFI subscales. Conclusions The Greek versions of the LARS score, COREFO and MSKCC-BFI questionnaires were proven to have good psychometric properties and can be used as specific and valid instruments for measuring LARS. Since the COREFO and MSKCC-BFI questionnaires, which are more extensive and possibly less applicable in routine clinical practice, showed no advantages in relation to the LARS score, the latter may be established as the simplest, fastest to complete and most targeted tool for assessing LARS.