Background: Research has shown that the body mass index (BMI) is not correlated with sperm retrieval outcomes, while serum testosterone and gonadotropins are related to the BMI in non-obstructive azoospermia (NOA). Previously, no comprehensive assessment had been conducted on the effect of the BMI of males in NOA. This study sought to comprehensively evaluate the effects of the BMI of males on hormone levels, sperm and embryo parameters, and clinical outcomes in NOA.Methods: The PubMed, Embase, Cochrane Library, and Web of Science databases were searched to retrieved relevant articles published up to May 27, 2022. Articles which examined patients with NOA (population), included patients with a BMI 225 kg/m2 (intervention) versus patients with a BMI <25 kg/m2 (comparator), assessed reproductive hormones, sperm and embryo parameters, and clinical outcomes (outcome), and were cohort studies (study design) were included. The quality of the included studies was assessed by the Newcastle-Ottawa Scale (NOS). A sensitivity analysis was conducted for all the outcomes.Results: A total of 12 studies comprising 2,994 NOA patients were included. Patients with a BMI 225 kg/m2 had lower follicle-stimulating hormone (FSH) [pooled weighted mean difference (WMD): -0.67, 95% confidence interval (CI): -0.94 to -0.41, P<0.001] and total testosterone (TT) (pooled WMD: -1.35, 95% CI: -2.10 to -0.60, P<0.001) levels than those with a normal weight (BMI <25 kg/m2). The testicular volume of the BMI 225 kg/m2 group was larger than that of the normal weight group (pooled WMD: 0.26, 95% CI: 0.09 to 0.44, P=0.003). The average BMI of the group with successful sperm extraction was lower than that of the group with failed sperm extraction (pooled WMD: -0.97, 95% CI: -1.89 to -0.04, P=0.041). The live -birth rate of the BMI 225 kg/m2 group was lower than that of the normal weight group [pooled relative risk (RR) =0.88, 95% CI: 0.78 to 0.99, P=0.031].Conclusions: The BMI of the males was an important factor affecting the FSH and TT levels, testicular volume, sperm retrieval success, and live-birth rate in NOA. Weight management may benefit NOA patients.