Background The mitochondrial displacement loop (D-loop) accumulates mutations and single nucleotide polymorphisms (SNPs) at a higher frequency than other regions of mitochondrial DNA (mtDNA).We previously identified disease riskassociated SNPs in the D-loop of chronic kidney disease (CKD) patients; in this study,we investigated the association of age-at-onset and D-loop SNPs in CKD patients.Methods The D-loop region of mtDNA was sequenced in 119 CKD patients attending the Fourth Hospital of Hebei Medical University between 2002 and 2008.The age-at-onset curve of the CKD patients was calculated using the KaplanMeier method at each SNP site,and compared using the log-rank test.Results The mean age of 119 CKD patients was (55.6±14.2) years,and 56.3％ were males.The mean estimated glomerular filtration rate (eGFR) was (81.2±12.4) ml·min-1·1.73 m-2,with 79.8％ (n=95) of patients having an eGFR ＜60 ml·min-1·1.73 m-2.All participants had an eGFR ＞30 ml·min-1·1.73 m-2.The age-at-onset for CKD patients who smoked was significantly lower than that of non-smoking CKD patients.The SNP sites of nucleotides 150C/T were identified for their association with age-at-onset using the log-rank test.The age-at-onset of patients with the minor allele T genotype was significantly lower than that of patients with the C genotype at the 150 SNP site (P=0.010).Conclusions Genetic polymorphisms in the D-loop appear to be predictive markers for age-at-onset in CKD patients.Accordingly,the analysis of genetic polymorphisms in the mitochondrial D-loop may help identify CKD patient subgroups at high risk of early onset disease.