Objective: To define the relative importance of fiber type as compared to laser wavelength on tissue injury depth, postoperative pain, and bruising during endovenous laser ablation. Methods: This study included 213 limbs that were treated with an 810-, 980-, or 1470-nm laser, with bare-tip (BT) or jacket tip (JT) fibers. Pain scores (10-point scale) and bruising scores (5-point scale) were recorded. Tissue thermal injury depth (mm) was evaluated in vitro for the 810- and 1470-nm wavelengths with BT and JT fibers. Results: The JT fibers had lower pain scores as compared to the BT fibers at 810 nm (1.69 +/- 1.77 vs 3.70 +/- 1.34; P < .0005) and at 980 nm (1.14 +/- 1.06 vs 2.71 +/- 1.80; P < .0005). The JT fibers had lower bruising scores as compared to the BT fibers at 980 nm (0.89 +/- 1.06 vs 2.00 +/- 1.44; P < .0005). The in vitro study showed lower thermal injury depths for the JT as compared to the BT fibers at 810 nm (0.36 mm +/- 0.26 mm vs 1.05 mm +/- 0.34 mm; P < .0005) and at 1470 tun (0.20 +/- 0.16 mm vs 0.71 +/- 0.31 mm; P < .0005). With regard to wavelength, 980-nm laser had lower pain scores as compared to 810-nm laser with BT fibers (2.71 +/- 1.80 vs 3.70 +/- 1.34; P = .015), and with JT fibers, a similar result trended toward significance (1.14 +/- 1.06 vs 1.69 +/- 1.77; P = .057). The 980-nm JT fiber showed less bruising as compared to the 810-nm JT fiber (0.89 +/- 1.06 vs 1.42 +/- 1.19; P = .019). Similarly, the 1470-nm JT fiber showed less bruising as compared to the 810-nm JT fiber (0.94 +/- 1.02 vs 1.42 +/- 1.19; P = .038). The in vitro study showed thermal injury depths that were less for 1470 nm as compared to 810 nm, with JT fibers (0.20 +/- 0.16 mm vs 0.36 +/- 0.26 mm; P = .013) or with BT fibers (0.71 +/- 0.31 mm vs 1.05 +/- 0.34 ram; P = .001). All mean differences between JT and BT fibers were greater than between differing wavelengths. The multivariate analysis for the in vitro study showed a mean difference between 1470 nm and 810 nm of 0.26 nun, P < .0005 favoring 1470 nm and a mean difference between JT and BT fibers of 0.61 mm, P < .0005 favoring the JT fibers. Conclusions: The use of a JT fiber appeared to be more significant in reducing pain and bruising as compared to a longer wavelength. Moreover, the results appeared additive, and the cohort using 1470 nm with a JT fiber produced the best treatment outcomes. Additional study is required to confirm the efficacy and durability of the various iterations evaluated; however, these data should be taken into consideration when undertaking treatment with endovenous laser ablation.