Introduction: The incidence of type 1 diabetes mellitus (T1DM) is increasing worldwide. Daily administration of multi-dose or single-dose Insulin therapy is the cornerstone in the treatment of T1DM. The recent studies highlighted the gap in knowledge, attitude, and practice (KAP) towards insulin therapy for the optimal control of hyperglycemia T1DM. The study aimed to assess knowledge, attitudes, and practices regarding insulin therapy among T1DM patients attending the diabetic clinic, Teaching Hospital Karapitiya (THK).Methods: A cross-sectional descriptive study was conducted using an interviewer-administered questionnaire to elicit socio-demographic information and KAP towards insulin therapy. A total of 62 attending the diabetic clinic at THK were recruited.Results: The study population consisted of 91.9% early young adults (ages 18-25 years) while the remainder represented late young adults (ages 26 - 30 years). A good knowledge, attitude and practice were seen in 61.3%, 62.9% and 38.1% of the patients respectively. Age, level of education, duration of DM, regular clinic visits and favourable attitudes were associated with good knowledge whereas level of education, duration of DM, regular clinic visits and good knowledge were associated with favourable attitudes. Duration of DM and regular clinic visits were the only factors associated with good practices. Higher level of knowledge or higher level of education were not associated with good practices towards insulin therapy (p>0.05).Conclusions & recommendations: Though majority had good knowledge and attitudes, practices were unsatisfactory in the majority of them. Self-management education and training giving special attention to psychosocial aspects of living to improve self-care behaviour are recommended to address the gap between knowledge and practices.