Background: Lesotho has the second-highest HIV and AIDS prevalence globally and is the country’s second leading cause of death. Despite increasing ART coverage, adolescents remain left behind and face high mortality because of delayed ART initiation. This study aimed to explore the experiences and challenges of nurses when initiating adolescents living with HIV on ART in Thaba-Tseka, Lesotho. Methods: A qualitative descriptive research design and twelve in-depth interviews were conducted among nurses from a hospital in the Thaba-Tseka district. Participants were selected purposively until data saturation was reached. Data were transcribed verbatim and analysed manually using the thematic analysis approach. The findings were presented in themes and sub-themes. Individual face-to-face interviews were conducted in English and Sesotho from May to August 2021. Results: The key findings in this study involved adolescents’ attendance at the health care facility, ART initiation process, HIV stigma influencing the uptake of ART, poor ART follow-up and socio-economic factors affecting adherence to ART. Conclusion: The themes uncovered in this study provide valuable insights into the gaps in ART initiation, and highlight the challenges encountered by nurses during this process among adolescents in Lesotho. The experiences and obstacles shared by nurses during ART initiation cover a range of issues, collectively demonstrating their engagement in HIV and ART care. These findings emphasise the critical role of policymakers and health care providers in devising customised ART initiation interventions for adolescents. Addressing these challenges will be crucial for enhancing ART uptake and adherence among adolescents living with HIV in Lesotho.