Objectives: This study investigates vocal outcome after cordectomy by transoral CO₂ laser microsurgery (TLM-cordectomy) in patients with laryngeal intra-epithelial neoplasia (LIN) or non-neoplastic lesions (NNL), for improved individual patient advice and potential adjustment of national treatment strategy by which patients suspected to have glottic LIN or T1a cancer are offered TLM-cordectomy, without prior biopsy. Study Design: Prospective, longitudinal, quasi-experimental time series. Methods: Consecutively included patients (n = 155) with LIN (n = 84) or NNL (n = 71) who underwent voice assessments before and after TLM-cordectomy. The multi-dimensional voice assessment protocol comprised voice and speech range profiles, aerodynamics, acoustic analysis, self-evaluated voice handicap, and perceptual auditory voice ratings. Results: Median follow-up time was 195 (range 50-1121) days for patients with LIN and 193 (range 69-1294) days for patients with NNL. Statistically significant changes, LIN: in voice handicap index (VHI) and breathiness after TLM-cordectomy. Statistically significant changes, NNL: voice range profile (voice range area, intensity range, and frequency range) and VHI after TLM-cordectomy. All group-wise changes were to less disordered voices. Previous smokers had the largest decreases in VHI and breathiness. Patients with baseline VHI scores >65 had smaller increases in VHI, however 13-19% of the patients had increases in VHI above the clinically relevant threshold after TLM-cordectomy. Conclusion: Overall, TLM-cordectomy in patients with LIN and NNL improved vocal outcome and our study thus supports the current Danish treatment strategy and improves the basis for proper patient advice. Multi-dimensional voice assessment is suggested preoperatively and six-nine months postoperatively, with focus on individual vocal differences and voice demands.