PURPOSE: Sex influences chemotherapy-induced nausea and vomiting (CINV). However, in clinical practice, males and females receive the same antiemetic prophylaxis. We compared CINV between sexes in patients with different emetic risk schemes and evaluated the predisposing factors and main adverse effects caused by antiemetics. METHODS: Prospective observational study conducted in a tertiary-care hospital from February 2023 to May 2024 in patients starting chemotherapy or a new treatment line. CINV was evaluated using MASCC antiemetic tool, in acute (<
24 h) and delayed phases (24-120 h). Results were analyzed using χ RESULTS: A total of 176 completed questionnaires (CQ): 94 for males and 82 for females were collected. The proportion of males who remained emesis-free was superior to females in the acute phase (100% versus 92.7%, p = 0.009). Likewise, a higher proportion of males remained nausea-free in the acute (91.5% versus 79.3%, p = 0.021) and delayed phase (90.4% versus 79.3%, p = 0.037). In females, young age (<
60 years) and previous nausea and vomiting during pregnancy may contribute to non-CR. A high proportion of patients reported adverse events like constipation and insomnia. Females suffered more constipation than males (52.4% versus 37.2%, p = 0.043). CONCLUSION: Females experienced more CINV than males, with the consequences that entail. Antiemetic prophylaxis should be personalized, considering sex and age and not only the chemotherapy emetic potential.