Introduction The Anorexia–Cachexia Syndrome (ACS) is a severe complication of cancer and is considered to be a significant cause of morbidity and mortality affecting up to two-thirds of cancer patients and one that needs specialized nursing care. Studies showed that the ACS has been relatively under-researched and under-resourced whist the nurses’ knowledge has not been systematically explored. Objective Τo explores nurses’ knowledge, understanding, and management of ACS in clinical practice in two European countries. Methods Descriptive-comparative study with 197 cancer nurses recruited during two National Conferences in Greece and Cyprus. Data were retrieved with the “Investigation of anorexia–cachexia syndrome in Practice” questionnaire. Results In terms of nurses’ perceptions on ACS, the prevailing characteristic reported in both countries was anorexia ( p = .65) followed by weight loss ( p = .04). 189 nurses (95.9%, p = .176) do not currently use a tool to assess patients’ nutritional status as part of their standard clinical practice. Statistically significant differences were found in relation to the routine assessment of nutritional-related symptoms including early satiety (Cyprus 64% vs. Greece 37%, p = .001), hiccough (66% vs. 36%, p < .001), alteration of the taste/odor sensation (77% vs. 45%, p < .001), problems in the oral cavity (84% vs. 68%, p = .032) and daily activities (85% vs. 69%, p = .032). The priority level for the ACS management differed significantly in the two countries ( p = .006), with higher priority being reported in Cyprus. Conclusion The study showed that more education is needed for cancer nurses to better understand the ACS which can facilitate the better management of the syndrome in clinical practice.