Objective. To analyze and explore the myths and beliefs about insulin therapy in patients with diabetes mellitus and their family caregivers from a general hospital in northern Peru in 2020. Materials and methods. This qualitative study used a thematic analysis model, following the interpretative paradigm. Sociodemographic and clinical data were obtained from medical records. Patients with diabetes that used some type of insulin for at least three months prior to the study were interviewed, as well as their family caregivers. Patients participated in a focus group and in-depth interviews; family caregivers participated only in in-depth interviews. Results. Twelve patients with diabetes (11 with type 2 diabetes mellitus) were included; six in the focus group and six in the in-depth interviews. Seven family caregivers were included. After analysis, we obtained four categories: 1) beliefs related to starting insulin treatment: treatment of choice after failure of other drugs, cures diabetes, regulates sugar, fear of injectables; 2) beliefs related to maintaining treatment: decompensation for not using insulin, insulin is necessary to live; 3) beliefs related to alternative therapies and cost: use of alternative therapies, high cost of insulin; and 4) myths related to the use of insulin: generates dependence, dependence for insulin administration, negative effects of insulin. Conclu-sions. The beliefs and myths of patients treated with insulin arise from the beginning of treatment, are maintained throughout the course of treatment, and are often reinforced by the worldview of family members. © 2023, Instituto Nacional de Salud. All rights reserved.