Purpose This first-in-human study evaluated telisotuzumab vedotin (Teliso-V), formerly called ABBV-399, an antibody–drug conjugate of the anti–c-Met monoclonal antibody ABT-700 and monomethyl auristatin E. Materials and Methods For dose escalation, three to six patients with advanced solid tumors were enrolled in eight cohorts (0.15 to 3.3 mg/kg). The dose-expansion phase enrolled patients with non–small-cell lung cancer (NSCLC) with c-Met–overexpressing tumors (c-Met positive; immunohistochemistry membrane H-score $ 150). Patients received Teliso-V monotherapy intravenously on day 1 once every 3 weeks. Safety, tolerability, pharmacokinetics, and maximum tolerated dose were determined. Results Forty-eight patients were enrolled (median age, 65 years; 35.4% NSCLC; median four prior therapies). One patient each in the 3.0-mg/kg (n = 9) and 3.3-mg/kg (n = 3) cohorts experienced dose-limiting toxicities. Although the maximum tolerated dose was not formally identified, the recommended phase II dose was defined as 2.7 mg/kg on the basis of overall safety and tolerability. The most frequent treatment-emergent adverse events (any grade) were fatigue (42%), nausea (27%), constipation (27%), decreased appetite (23%), vomiting (21%), dyspnea (21%), diarrhea (19%), peripheral edema (19%), and neuropathy (17%). The most frequent Teliso-V–related grade $ 3 adverse events were fatigue, anemia, neutropenia, and hypoalbuminemia (4% each). Teliso-V and total antibody pharmacokinetics were approximately dose proportional, with a mean harmonic half-life of 2 to 4 days each. Prospective screening identified 35 (60%) of 58 patients with c-Met–positive NSCLC. Of 16 patients with c-Met–positive NSCLC who were treated with Teliso-V 2.4 to 3.0 mg/kg, three (18.8%; 95% CI, 4.1% to 45.7%) achieved a partial response (median response duration, 4.8 months; median progression-free survival, 5.7 months; 95% CI, 1.2 months to 15.4 months). No other patients experienced a response. Conclusion Teliso-V monotherapy demonstrated favorable safety and tolerability profiles, with encouraging evidence of antitumor activity in patients with c-Met–positive NSCLC.