Laser- or light-assisted therapies have been used to improve the perifollicular environment by upregulating the expression of growth factors and signaling molecules for hair restoration. The aim of our study was to preclinically and clinically evaluate the therapeutic efficacy and safety of a 1927-nm fractionated thulium laser on pattern hair loss (PHL). An in vivo hairless mouse study and an in vivo human skin environmental scanning electron microscopy (ESEM) study were performed with different power and energy settings. Thereafter, an evaluator-blinded, split-scalp study was conducted to evaluate hair thickness and density in 10 PHL patients treated with 12 sessions of fractionated thulium laser treatment with or without post-laser treatment application of a growth factor-containing (GF) solution. In in vivo hairless mouse skin, inverted cone-shaped zones of thulium laser-induced tissue coagulation (LITC) were noted immediately after treatment in the epidermis and upper to mid-dermis without remarkable ablative tissue injury. The ESEM study revealed round to oval-shaped zones of non-ablative LITC on the surface of the stratum corneum of a human subject immediately after laser irradiation. In PHL patients, 12 sessions of thulium laser monotherapy at 1-week intervals resulted in significantly increased hair density and thickness. Post-laser treatment application of GF solution offered additional therapeutic efficacy by improving hair density and thickness on the split scalp. The use of a fractionated thulium laser with or without post-laser therapy application of GF solution to treat PHL elicited remarkable improvements in hair thickness and hair counts.