Objective To predict the causal relationship between immune cells and osteomyelitis(OM)by using Mendelian randomization.Methods Data sets of 731 immune cells and osteomyelitis were obtained from the UK Biobank and the genome wide association study.The inverse variance weighted method,weighted median method,and MR-Egger method were employed sequentially to verify the causal relationship between the 731 immune cells and osteomyelitis.Cochran's Q test,MR-Egger intercept test,mendelian randomization pleiotropy residual sum and outlier(MR-PRESSO),and leave-one-out analysis were evaluatede the stability and reliability of the results.Results A total of 21 immune cells were found to have a causal relationship with osteomyelitis(P＜0.05).Among them,T regulatory cells,classical dendritic cells and B cells were exhibited more stable causal relationships with osteomyelitis(P＜0.01).Specifically,T regulatory cells(OR=0.925,β=0.078)were identified as protective factors reducing the risk of osteomyelitis,while classical dendritic cells(OR=1.084,β=0.081)and B cells(OR=1.063,β=0.061)were identified as risk factors increasing the risk of osteomyelitis.Conclusion Twenty-one immune cells are genetically associated with the risk of osteomyelitis.