Research question: Is acrosin activity related to cumulative live birth rate (CLBR) over 1 year after IVF, intracytoplasmic sperm Design: Retrospective monocentric cohort study of 5704 couples who started IVF/ICSI treatments between 2016 and 2021. Acrosin activity was determined by a modified Kennedy method using a commercial kit. Patients were divided into two groups according to their acrosin activity: below 25 mu IU/106 spermatozoa; and an acrosin activity 25 mu IU/106 spermatozoa or above. Primary outcome was the CLBR, defined as an ongoing pregnancy leading to live birth that had arisen from all embryo transfers carried out within 1 year after the first ovum retrieval. Both conservative and optimistic methods were used for estimating CLBRs. Results: The CLBRs of patients with an acrosin activity below 25 mu IU/106 spermatozoa were found to be significantly lower than those of patients with an acrosin activity 25 mu IU/106 spermatozoa or above by conservative (48.5% versus 55.4%, P = 0.02) and optimistic (63.7% versus 70.3%, P = 0.047) methods after adjusting for confounders. When acrosin activity was regarded as a continuous variable, significant negative relationships between acrosin activity and CLBR were identified in subgroups: young couples (men and women aged younger than 30 years) and couples from whom no more than 10 eggs were retrieved. Conclusion: Low acrosin activity levels were correlated with decreasing CLBRs over 1 year. These findings suggest that acrosin activity can be used as a predictor for CLBRs before starting IVF/ICSI treatment to enhance the effectiveness of counselling.