AIM To assess the predictive and prognostic value of neurofibromin (NF) expression in colorectal carcinoma (CRC). MATERIALS AND METHODS The present series consists of archival samples from 191 patients with stage I, II, III, or IV CRC treated between 1981 and 1990 at the Turku University Hospital (Finland). Tumor biopsies as microarray blocks were analyzed for expression of NF by immunohistochemistry. Different grading systems were tested for NF expression. RESULTS A significant correlation between NF expression and tumor localization was found, with tumors arising in the colon showing intense NF expression more often than those arising in the rectum (p=0.014). Higher expression of NF was more common in tumors not responding to treatment (p=0.004). Tumors with multiple metastases showed higher expression of NF than those with single metastasis only (p=0.025). Furthermore, NF expression showed a borderline (p=0.068) correlation with gender; tumors of women showed higher NF expression that those of males. On the other hand, NF expression was not significantly associated with tumor recurrence, age, lymph node involvement, tumor grade and tumor stage or disease outcome. CONCLUSION Positive NF expression in CRC is a sign of aggressive disease and poor outcome.