<b><i>Background:</i></b> Fatigue is a common distressing symptom for patients living with chronic or acute diseases, including liver disorders and cancer (<i>Cancer-Related Fatigue</i>, CRF). Its etiology is multifactorial, and some hypotheses regarding the pathogenesis are summarized, with possible shared mechanisms both in cancer and in chronic liver diseases. A deal of work has investigated the role of a multifunctional molecule in improving symptoms and outcomes in different liver dysfunctions and associated symptoms, including chronic fatigue: S-adenosylmethionine (SAM; AdoMet). The aim of this work is actually to consider its role also in oncologic settings. <b><i>Patients and Methods:</i></b> Between January 2006 and December 2009, at the University Campus Bio-Medico of Rome, 145 patients affected by colorectal cancer in adjuvant (<i>n</i> = 91) or metastatic (<i>n</i> = 54; <i>n</i> = 40 with liver metastases) setting and treated with oxaliplatin-based regimen (FOLFOX for adjuvant and bevacizumab + XELOX for metastatic ones), 76 of which with the supplementation of S-adenosylmethionine (AdoMet; 400 mg b.i.d.) (57% of adjuvant patients and 44% of metastatic ones) and 69 without AdoMet supplementation, were evaluated for fatigue prevalence using the Functional Assessment of Chronic Illnesses Therapy-Fatigue (FACIT-F) questionnaire, at 3 and 6 months after the beginning of oncologic treatment. Notably, the number of patients with liver metastases was well balanced between the group of patients treated with AdoMet and those who were not. <b><i>Results:</i></b> Among patients receiving oxaliplatin-based chemotherapy, both in adjuvant and in metastatic settings, after just 3 months from the beginning of chemotherapy, mean scores from questionnaire domains like FACIT-F subscale (7.9 vs. 3.1, <i>p</i> = 0.006), FACIT physical (6.25 vs. 3.32, <i>p</i> = 0.020), FACIT emotional (4.65 vs. 2.19, <i>p</i> = 0.045), and FACIT-F total score (16.5 vs. 8.27, <i>p</i> = 0.021) were higher in those receiving supplementation of AdoMet, resulting in reduced fatigue; a significant difference was maintained even after 6 months of treatment. <b><i>Discussion and Conclusions:</i></b> Mechanisms and strategies for managing CRF are not fully understood. This work aimed at investigating the possible role of S-adenosylmethionine supplementation in improving fatigue scores in a specific setting of cancer patients, using a FACIT-F questionnaire, a well-validated quality of life instrument widely used for the assessment of CRF in clinical trials.