The associations between single nucleotide polymorphisms (SNPs) in the displacement loop (D-loop) of mitochondrial DNA (mtDNA) and cancer risk and disease outcome have been extensively analyzed. We investigated the association between age-at-onset and SNPs in the mitochondrial D-loop using a population-based series of non-small cell lung cancer (NSCLC) patients. The D-loop region of mtDNA from NSCLC patients was amplified and sequenced. The age-at-onset curve of NSCLC patients was calculated using the Kaplan-Meier method at each SNP site and values were compared using the log-rank test. The SNP sites of nucleotides 200G/A and 16362T/C were identified to determine their association with age-at-onset of NSCLC using the log-rank test. The nucleotide 207G/A was identified for its association with age-at-onset at a borderline significance level (P = 0.060). We found that genetic polymorphisms in the D-loop were predictive markers for age-at-onset in NSCLC patients. Accordingly, the analysis of genetic polymorphisms in the mitochondrial D-loop can be used to identify NSCLC patient subgroups at high risk of early onset.