Background: Molecular testing practices and cost-sharing policies may result in delayed initiation of TKI therapy. We assessed predictors of delayed initiation of TKIs in metastatic EGFR+ or ALK+ NSCLC. Methods: We identified patients with EGFR+ and ALK+ NSCLC diagnosed between 01/01/2010 and 12/31/2016 in the Washington State SEER registry using validated natural language processing methods. We linked registry records to commercial and Medicare (including part D) claims. Eligible patients had stage IV NSCLC, sensitizing EGFR mutations or ALK+ by FISH, ≥ 1 pharmacy claims for EGFR or ALK TKIs, and ≥12 months of insurance enrollment post-diagnosis. Potential predictors included age, sex, race, Census-level median household income, urban status, insurance type, comorbidity, histology, mutation type, and receipt of chemotherapy prior to first TKI claim (pre-TKI chemo). We defined time to TKI initiation as the interval from diagnosis to first pharmacy claim for EGFR or ALK TKIs. We fitted Cox regression models to identify predictors of delays in TKI initiation, defining covariates with a P < 0.05 in a final multivariate model as independently associated with delays. Results: For 122 patients (median age 70; 65% female; 74% White; median income $66,580; 98% metropolitan; 35% Medicare; 80% EGFR+; 12% using pre-TKI chemo), the median time to TKI initiation was 6.7 weeks (IQR = 3.9 to 14.0). Independent predictors of TKI delays included male sex (HR = 0.51; 95%CI = 0.34; 0.76); Medicare insurance (HR = 0.32; 95% CI = 0.20; 0.53) and pre-TKI chemo (HR = 0.37; 95% CI = 0.20; 0.66). Median time to TKI initiation was 9.7 vs. 5.8; 7.8 vs. 4.1; and 16.0 vs. 6.3 weeks in male vs. female, Medicare vs. commercial insurance, and pre-TKI chemo (yes vs no), respectively. Conclusions: Male sex, Medicare insurance, and chemotherapy prior to TKI are associated with delays in TKI initiation for EGFR+ and ALK+ stage IV NSCLC patients. Possible explanations include higher prevalence of smoking in males resulting in lower priority for molecular testing, high cost-sharing policies for TKIs in Medicare patients, and prolonged time to obtain molecular test results leading patients to start chemotherapy first.